Flash

Flash is a 'targeted' summoner spell and activates instantly upon being cast, warping the player's champion toward his/her cursor. It is often nicknamed as "Blink" by players.

Strategy
Flash can easilly be used to escape from or catch up with a foe. It can also be used to dodge or land skill shots. Another use for this spell is to "wall jump", where you use flash to hop over a wall, which can drastcially decrease the path you would otherwise need to travel.

Trivia

 * For a time, the inclusion of flash in the game was hotly debated and Riot strongly considered removing Flash from the game entirely, with players both for and against removal. In V1.0.0.107, Flash was nerfed with an increased cooldown from 240 to 255. The ability to pop incoming projectiles was also removed. Since then, no additional changes have been made or announced about its potential removal.