Zerging describes a tactic, originating in MMORPGs but used in many different computer games, that is analogous to the human wave attack in real-world ground warfare, in which overwhelming numbers of troops are sent at the enemy. Zerging in MMORPGs carries the connotation of a disorganized attack that relies upon superior numbers and levels to win. It is analogous to the Zergling Rush from Starcraft. A body of players or army involved in a zerg is collectively referred to as a "zerg", while a player who participates in zerging (is part of the zerg) is often called a Zergling.

The word "zerging" carries a negative or derogatory connotation, as it is characterised by hurling vast quantities of troops at the enemy without consideration of tactics or casualties. Many MMORPG encounters are specifically designed with "anti-zerg" features, such as wide-area attacks, that can severely damage a large uncoordinated group. Despite its specific origins, zerging is used in many games, from Warhammer (regarding horde armies) to Everquest (describing an attack in which large numbers of participants are simply thrown at the opponent). In MMOs, a guild or clan that recruits players en masse (to increase zerging effectiveness) is often termed a zerg guild.

Zerging can refer to a wide range of army sizes, ranging from a 10 man group in a 5 man dungeon, to a 100 man PvP raid. In general, any army that is perceived as "too big" for the challenge it is undertaking can be called a zerg. Instance zerging is a very common tactic in World of Warcraft, wherein 10 players will clear out a 5 man instance dungeon such as Blackrock Depths or Scholomance. Instance zerg tactics are encouraged by the fact that, in general, all the good loot is at the end of a dungeon. Whereas a 5 man group could wipe before it finishes the dungeon, a 10 man group can complete the dungeon and obtain good loot very easily.

Despite its effectiveness, zerging is generally considered unsporting, as it allows a large number of players with less skill to overcome a challenge that should require a much higher skill level. However, it remains a highly effective tactic, and is often the only way for lower level players to overcome a higher level challenge.