League Of legends Wiki - Roles - The Jungler
Jungling is the practice of killing neutral "Monsters" located on the maps between the lanes. The Jungle refers to any area of the map that is not a lane or part of either team's base, including the river that divides it. Junglers rely on killing neutral monsters in the jungle to keep up with their laning teammates in terms of gold and experience. In a standard 5-on-5 game of League of Legends, 4 players on a team will be Laners, and 1 player will be a designated Jungler. A ganking jungler aims to contribute to his team by providing constant pressure to enemy laners and setting up kills for their allies allowing them to snowball their way to victory even as the ganker jungler falls behind in gold due to generally low farm. Such junglers often tend to prioritize heavy crowd control and mobility in their kit, which allows them to reach even the most heavily-entrenched laners and lock them down long enough to ensure their demise. Ganker junglers tend to be good picks against farming junglers, as without the need to worry about an opponent intercepting a gank attempt they can freely roam and harass opposing laners with no fear of reprisal. There are other important tasks that a jungler is able to perform, due to their roaming nature preventing enemy champions from spotting the jungler through the fog of war. This allows for unexpected positioning and surprise attacks, mainly through the use of ganks. Their ability to freely traverse the map without being tied to a lane also allows them to support lanes when in the area, such as warding key locations without forcing someone else to abandon their lane and coming to an ally's aid when they come under duress.