A kind of bicycle race. Familiar to those interested in bicycle racing.
Criteriums generally consist of many laps around a short closed circuit, usually not more than 1 mile long. Because it is easier to close a few city blocks than ~75 miles of roads to automobile traffic.
Because of its nature, criteriums (or crits) are good for spectators. Also, they are quite different to road races, because there can be no long inclines. If any hills are present, they tend must be short. The pain comes from having to climb the short hill 60 times in 60 minutes.
Because it is hard to break away in these kind of races, they are spiced up by primes (pronounced "preems", at least in Seattle). These are special mid-race sprints, offering a prize to the next person accross the finish line.
This kind of race puts a premium on bike handling skills due to the constant turning which usually occurs on criterium courses.
In the past, they were the primary money-making mechanism for successful bicycle racers. Famous racers and winners of major races (like the Tour de France) would be paid significant amounts of money to appear at late season crits. For instance, Eddy Merckx used to reward his teammates for their service by demanding that his teammates also be paid to appear at these races.