Conditions

Conditions (aka "Status Effects") alter a creature's capabilities in a variety of ways and can arise as a result of a spell, a class feature, a monster's attack, or other effect. Most conditions, such as blinded, are impairments, but a few, such as invisible, can be advantageous.
A condition lasts either until it is countered (the prone condition is countered by standing up, for example) or for a duration specified by the effect that imposed the condition.
If multiple effects impose the same condition on a creature, each instance of the condition has its own duration, but the condition's effects don't get worse. A creature either has a condition or doesn't.
Some conditions are included in other conditions. For example, an Unconscious creature is also considered Incapacitated.
The list of conditions are as follows:

Bleeding

A Bleeding creature loses Hit Points at the end of each of their turns in combat, or every hour outside of combat.
There are 6 "levels" of Bleeding:

1. Lose 1d4 Hit Points every round, or 1d6 Hit Points every hour
2. Lose 1d8 Hit Points every round, or 1d10 Hit Points every hour
3. Lose 1d12 Hit Points every round, or 2d12 Hit Points every hour
4. Lose 2d12 Hit Points every round, or 4d12 Hit Points every hour
5. Lose half your maximum Hit Points every round, or your Hit Points become 0 and are dying every hour
6. Death

Bleeding creatures also cannot gain the benefits of a Long Rest unless the Bleeding is staunched, and creatures with Keen Smell have Advantage on checks made to track a Bleeding creaure. However, Bleeding creatures do not automatically fail Death Saves but also cannot be stabilized until the Bleeding is staunched or the creature regains Hit Points.
Creatures lose 1 Bleeding level after completing a Long Rest.

Blinded

While you have the Blinded condition, you experience the following effects.
Can't See
You can't see and automatically fail any ability check that requires sight.
Attacks Affected
Attack rolls against you have Advantage, and your attack rolls have Disadvantage.
Creatures with abilities such as Blindsight or Tremorsense can overcome the Blinded condition out to a certain range, but they still cannot physically "see" anything, they only know where something is located within its Blindsight or Tremorsense range. If it seems like a creature can still see you despite being Blinded, maybe they have one of these senses!

Charmed

While you have the Charmed condition, you experience the following effects.
Can't Harm the Charmer
You can't attack the charmer or target the charmer with damaging abilities or magical effects.
Social Advantage
The charmer has Advantage on any ability check to interact with you socially.

Deafened

While you have the Deafened condition, you experience the following effect.
Can't Hear
You can't hear and automatically fail any ability check that requires hearing.

Exhaustion - REQUIRES DISCUSSION

Some special abilities and environmental hazards, such as starvation and the long-term effects of freezing or scorching temperatures, can lead to a special condition called Exhaustion, measured in "points".
Exhaustion points range from 0 to 12. Every point of exhaustion reduces any d20 roll (excluding Death Saves) by the number of Exhaustion points the character has. Certain levels of exhaustion also carry stacking side effects:

Exhaution Points	Additional Penalty
1	none
2	-5ft Speed
3	-1 AC
4	-10ft Speed
5	none
6	-2 AC
7	-15ft Speed
8	all Non-Racial & Non-Magical Speed Buffs LostA
9	-3 AC
10	Speed Becomes 0
11	Unconscious
12	Death

A - Examples including, but not limited to:

Barbarian "Fast Movement" (Level 5)

Monk "Unarmored Movement" (Level 2)

Ranger "Deft Explorer Improvement - Roving" (Level 6)

Frightened

While you have the Frightened condition, you experience the following effects.
Ability Checks and Attacks Affected
You have Disadvantage on ability checks and attack rolls while the source of fear is within line of sight.
Can't Approach
You can't willingly move closer to the source of fear.

Grappled

While you have the Grappled condition, you experience the following effects.
Immobile
Your Speed is 0 and can't increase.
Attacks Affected
You have Disadvantage on attack rolls against any target other than the grappler.
Movable
The grappler can drag or carry you when it moves, but every foot of movement costs it 1 extra foot unless you are Tiny or two or more sizes smaller than it.

Grappling

A Grappling creature is inflicting the "Grappled" condition on another creature. A Grappling creature must have at least one applicable limb available at all times to sustain the "Grappled" condition on each creature it is Grappling, and that limb cannot be used for anything else during that time. If that limb stops being used to sustain the "Grappled" condition for any reason, whether the Grappling creature was willing or not, the "Grappled" condition immediately ends for the affected creature. Some creatures have special actions they can take on creatures "Grappled" by them which do not end the 'Grappled' condition.
It is not possible to grapple a creature more than 1 size category larger than you. For example, a Small creature cannot grapple a Large creature. Additionally, creatures at least 2 size categories larger than their target have advantage on their Strength (Athletics) checks to maintain a grapple.
There is effectively no limit on how many creatures can be "Grappled" by one creature, so long as the creature has a sufficient number of limbs.

Incapacitated

While you have the Incapacitated condition, you experience the following effects.
Inactive
You can't take any Action, Bonus Action, or Reaction.
No Concentration
Your Concentration is broken and you cannot begin Concentration on anything while you have this effect.
Speechless
You can't speak.
Surprised
If you're Incapacitated when you roll Initiative, you have Disadvantage on the roll.

Invisible

While you have the Invisible condition, you experience the following effects.
Concealed
You aren't affected by any effect that requires its target to be seen unless the effect's creator can somehow see you. Any equipment you are wearing or carrying is also concealed.
Attacks Affected
Attack rolls against you have Disadvantage, and your attack rolls have Advantage. If a creature can somehow see you, you don't gain this benefit against that creature.

Paralyzed

While you have the Paralyzed condition, you experience the following effects.
Incapacitated
You have the Incapacitated condition.
Immobile
Your Speed is 0 and can't increase.
Saving Throws Affected
You automatically fail Strength and Dexterity saving throws.
Attacks Affected
Attack rolls against you have Advantage.
Automatic Critical Hits
Any attack roll that hits you is a Critical Hit if the attacker is within 5 feet of you.

Petrified

While you have the Petrified condition, you experience the following effects.
Turned to Inanimate Substance
You are transformed, along with any nonmagical objects you are wearing and carrying, into a solid inanimate substance (usually stone). Your weight increases by a factor of ten, and you cease aging.
Incapacitated
You have the Incapacitated condition.
Immobile
Your Speed is 0 and can't increase.
Attacks Affected
Attack rolls against you have Advantage.
Saving Throws Affected
You automatically fail Strength and Dexterity saving throws.
Resist Damage
You have Resistance to all damage.
Poison & Disease Stasis
You have Immunity to the Poisoned condition. You also stop being affected by poisons and diseases and cannot contract new diseases until your petrification ends.

Poisoned

While you have the Poisoned condition, you experience the following effect.
Ability Checks and Attacks Affected
You have Disadvantage on attack rolls and ability checks.

Prone

While you have the Prone condition, you experience the following effects.
Restricted Movement
Your only movement options are to crawl or to spend an amount of movement equal to half your Speed (round down) to right yourself and thereby end the condition. If your Speed is 0, you can't right yourself.
Attacks Affected
You have Disadvantage on attack rolls. An attack roll against you has Advantage if the attacker is within melee attack range of you. Otherwise, that attack roll has Disadvantage.

Restrained

While you have the Restrained condition, you experience the following effects.
Immobile
Your Speed is 0 and can't increase.
Attacks Affected
Attack rolls against you have Advantage, and your attack rolls have Disadvantage.
Saving Throws Affected
You have Disadvantage on Dexterity saving throws.

Stunned

While you have the Stunned condition, you experience the following effects.
Incapacitated
You have the Incapacitated condition.
Saving Throws Affected
You automatically fail Strength and Dexterity saving throws.
Attacks Affected
Attack rolls against you have Advantage.

Surprised

If a creature is caught unawares by the start of combat, that creature is surprised, which causes it to have Disadvantage on its Initiative roll.

Unconscious

While you have the Unconscious condition, you experience the following effects.
Inert
You have the Incapacitated and Prone conditions, and you drop whatever you're holding. When this condition ends, you remain Prone.
Immobile
Your Speed is 0 and can't increase.
Attacks Affected
Attack rolls against you have Advantage.
Saving Throws Affected
You automatically fail Strength and Dexterity saving throws.
Automatic Critical Hits
Any attack roll that hits you is a Critical Hit if the attacker is within 5 feet of you.
Unaware
You're unaware of your surroundings.