zZ

zz is a two-letter string that appears in a variety of contexts and does not have a single, universal meaning. In everyday writing and cartoons, "zz" (often extended to "zzzz") is a conventional shorthand for sleep or snoring, implying someone is asleep.

In biology, ZZ denotes a specific chromosomal genotype in species that use the ZW sex-determination system. In these organisms, males typically carry two Z chromosomes (ZZ), while females carry one Z and one W (ZW). This usage is relevant to birds, some reptiles, and certain fish; it is not applicable to mammals, which use the XY system.

In popular culture, ZZ Top is a famous American rock band formed in 1969 in Houston, Texas. The name is often styled as ZZ Top and has entered common usage as a shorthand reference to the band in media.

Because "zz" can refer to different things depending on context, its meaning should be inferred from surrounding information. It may indicate sleep, a biological genotype, or a proper noun such as a brand or group name.