Role

A role within Dota 2 defines the way a Hero can be played given their Attributes and Skills; different Heroes are suited for different roles. It is important to have a variety of roles in a team in order to increase the tactics at your disposal. There are three major roles: Ganker, Support and Carry; every hero can atleast fullfill one of these. There are lesser, more subtle roles too: Pusher, Tank, Roamer, or Jungler are a few examples.

Carry
Carry heroes are heroes with strong damage potential, but require expensive items to perform well. They are usually paired in lane with a support that can help them farm with ease, and let them get the kills if the chance arises. Their name comes from the fact that late in the game, if they have gained a lot of gold, they can "carry" their team to victory.

Ganker
Ganker type heroes usually have mobility impairing abilities, and they roam from lane to lane looking for unaware enemies to help their teammates kill them. Usually these heroes have strong Attributes and Abilities, and barely depend on items.

Support
Support heroes provide help to their team, healing or buffing them, or damaging and debuffing the enemies. They usually purchase aura items or items with active abilities that further increase their variety of disabling spells. Their job is to help the carry farm and get kills, so they can become strong enough to win the game.