Term: Attack
An Attack, sometimes called a Strike, is the use of a weapon (or similar, such as a Natural Weapon) to hit, and damage, an enemy.
Attacks are generated with the Attack Action | ◈◈ / ◈-◈◈◈. Some features, such as Additional Attack generate an extra Attack.
When you spend your attack, you will roll a d20 and add your Attack Modifier, or the Attribute used with the Attack, plus your Proficiency Bonus. You roll against a target's Armor Class / AC, comparing the result. The weapon and/or Ability will have the damage and whatever else is needed to calculate Damage. If you land a Critical Success (sometimes called a Critical Hit, done by rolling +10 over the AC, or rolling a natural 20), you deal the damage the weapon deals again (practically doubling the damage).
Some Maneuvers will use an Attack instead of (or in addition to) costing Actions.