Variant histone H2A which replaces conventional H2A in a subset of nucleosomes. Nucleosomes wrap and compact DNA into chromatin; limiting DNA accessibility to the cellular machineries which require DNA as a template. Histones thereby play a central role in transcription regulation; DNA repair; DNA replication and chromosomal stability. DNA accessibility is regulated via a complex set of post-translational modifications of histones; also called histone code; and nucleosome remodeling. May be involved in the formation of constitutive heterochromatin. May be required for chromosome segregation during cell division. {ECO:0000269|PubMed:15878876}.