Matchmaking
The service that assembles players into online matches based on skill, latency and waiting time.
Blizzard's Battle.net (1996) was early in simply letting players find each other. Modern systems trade off three things: even skill, low latency and a short queue. Skill is measured with rating systems like Elo, borrowed from chess, or Microsoft Research's TrueSkill, built for Xbox Live and able to handle teams and more than two players. The queue then loosens its criteria gradually until someone fits.
Skill-based matchmaking, SBMM, is contentious. Even matches are fair but exhausting — every evening becomes a sweaty final — and players have long suspected the systems match on spending habits too. Matchmaking also decides which server or host a match lands on, and therefore whether a listen server hands someone an edge.