Nobody likes to play support, yet everbody likes to win - Bastion
In DotA2, there are basically 2 types of heroes : Carries and Supports. Carries are the heroes that have tremendous damage and can easily wipe out the other teams heroes. Supports on the other hand are the ones that help the carries eliminate the other team; be it their skills, their items or their actions. These heroes usually rely on spells ranging from disables, AoEs, damage spells, etc. These skills usually do not affect the enemy heroes anymore in the endgame.