Starcraft is a real-time strategy game, and Zerg is one of three factions you can play in the game. Zerg units are individually weak but cheap compared to the other factions, so Zerg players typically compose swarms of disposable units when staging and conducting attacks. It’s also quicker to make large swarms, since there isn’t a sequential build queue for Zerg unit construction. It makes for a pretty interesting switch in mindset compared to the other sides, where there is much more emphasis on preserving one’s units. Some of the more obnoxious strategies, like the Zerg rush, have become memes among gamers.