In online gaming, the term ganking means an ambush on another player.
The definition of a gank depends mostly on the game in which the act occurs. For example, in battle-arena games such as Defense of the Ancients, ganking means several teammates quickly killing one member of the enemy team while the rest of the enemy team is not nearby. In MMORPGs such as World of Warcraft, ganking usually means a high-level player killing a low-level player; oftentimes, there is no chance of the low-level player winning.
Opinions vary on the latter form of ganking; some see it as legitimate gameplay, others view it as cowardly.