To assure ones victory using overwhelming numbers.
To greatly outnumber the enemy, and swarm them.
To trivialize en encounter using mass numbers of allies rather then skill
That guild zerged us.
Those guys are a bunch of zerglings.
Nowadays term zerg is used in mmo games to describe force consisted of large group of lower level players (often with only basic equipment) who use numbers rather then strategy to defeat the enemy, therefore requiring no skill. This tactics is commonly known as zerging
In MMORPG's a popular way to beat a battle is by using overwhelming numbers, and the term zerging was borrowed from starcraft to define this. This can often accomplish a feat with minimal skill and or gear, however many games now take this into effect and design encounters so that after a certain threshhold of players it becomes more difficult to manage the encounter. For example, a few well placed hidden pits around a boss that when someone falls into them it releases a wave of ravenous creatures against the raid. In this case having a hundred people almost completely ensures that some idiot will fall into the traps no matter how many times you tell everyone where they are and how not to fall into them.
In other MMORPG's which are player vs player zerging is often seen when one team or player is playing so far above the other teams that the losing side finally builds up a force large enough to win purely by flesh count. DAOC was a game where this occured often by placing barriers to PVP that forces could camp. If the force camping the bottleneck into the frontiers was good then it would do one of two things. 1. It could demoralize the enemy and shut down RVR. 2. It would create a buildup of players behind the bottleneck that would eventuall form a zerg.
Zergs were considered by some a necessary evil in DAOC, but many considered them a design flaw in the game.
Human Vs. Zerg.
Building SCV (harvester) units.
Two zerglings (basic zerg fighter) attack before your first marine (basic human fighter) is built. You may attack the zergings with your SCV units, and will likely kill them, but at a cost of the life of an SCV unit or two. After a brief time you may get a marine or two built, but then six zerglings attack, and instead of attacking the marines they attack only the SCV units. The zerglings are weak and die quickly but may take out another couple SCV units. After another brief time the humans are trying to create more SCV units to boost production to a much needed level instead of creating more defenses when the next wave of 12 zerglings come in and decimate the remaining SCV units. As expected within minutes the game is over when the humans are overrun with waves of zerglings who have never had a shortage of raw materials.
EQ zerging: We are going to zerg rush the Avatar of War. - 30 minutes later the entire zone floor is covered in corpses, and the Avatar of War is standing above a hunred corpses like nothing ever happened.
From the Hibernians: I can't believe our 8 person group was fighting honorably when those Albion's came over the hill with a hundred people and frickin zerged us.
From the Albions: Cry moore noob hibblets.