Elementals

The term 'elemental' is terribly imprecise. It simply refers to a creature that isn't from the world of Senkar, and one which is subject to summoning and banishment.
Elementals can be summoned either into the world or, by the use of atavism, into the mind of the summoner.
Elementals vary considerably. On one hand, you have unintelligent creatures that are driven purely by instinct, and on the other, you have highly intelligent, sophisticated ones that can put the finest minds of Selwyn to shame. Most of these beings don't much care about mortals, but a surprisingly large percentage can be actively malevolent. Elementals from demonic planes often like to capture magi then use them as breeding stock to provide a mana source.
The behavior and personality of an elemental often reflect its type. Most nature elementals are merely plants and animals that dwell on other planes of existence, often with strange and unusual appearances. More rarely, fey can be summoned, from dryads to nymphs, satyrs, or rarely, the wild fey. However, fey are… capricious. Another example is lightning elementals, which have one hell of a temper.
The rank of an elemental is a rough estimation of their power. It's meant to equate to the circle of magic they would be able to use as a mage, but as not all elementals are capable of casting spells, it's not perfect. Most elementals aren't terribly powerful, but those who are at least fifth rank are rather impressive. They're often somewhat stronger than a mage who only has reached fifth circle in a single sphere.
When people from Senkar travel to other planes, then by definition they are elementals. Beings from Senkar can be banished from other worlds but - for reasons not understood - cannot be summoned to them.