Summoning

Unlike a Phantasm which is a manifestation of a mage's magical power, a summon is a creature already in existence often bound to their summoner either through force or by choice.

The idea behind summoning is quite a simple one; take a creature from somewhere else, usually another plane of existence though the same plane is not uncommon, and bring it to a specific spot.

This can be done for a variety of reasons, including (but by far not limited to) trying to trap a creature by summoning it into a place where that is possible, attempting to bargain with a creature, attempting to bind a creature into service, and attempting to banish a creature (this is usually where summoning something in the same plane of existence comes into play).

However this does not come without its drawbacks, and many summoners end up in over their heads. Their bindings or banishments aren't sufficient and whatever creature they bring into the world kills them before moving on. Tragic, and yet a lesson that is learned the hard way despite all the warnings that those individuals choose to ignore.