Instant

An instant is a spell or ability with a cast time of zero.

In practice, instant means less than half a second but seems to depend on server response. Typically such spells can be cast on the move, which can serve as a great advantage over spells that must be cast while standing still. Instant cast spells come in many forms including DoTs such as Shadow Word: Pain and a Warlock's curses, heal-over-time spells such as Renew, and instant damage spells such as a Shaman's Earth Shock. Instant cast spells are distinct from channelled spells, which although cast instantly must then be channelled in order to take effect, and can be interrupted before their full effect is complete.