Relevos Atómicos or simply Atómicos are eight man tags with two teams of four luchadors.
Unless other stipulations are applied, Atomicos work under normal lucha libre captian's rules. One wrestler is designated as the captain and the fall or match is immediately over if they are defeated. The match is also over if all three non-captains are beat, though sometimes the rule is relaxed to only require two non-captians losing. In practice, Atomicos are simply about getting one more particpant on to a trios team.
Atomicos are a standard of AAA. The Mexican National Atomicos Championship was initiated by that promotion and has always resided there. Atomicos are run frequently, including some Relevos Triple A variants.
CMLL rarely runs atomicos. Other groups may run them from time to time.