Plasma membrane-associated small GTPase which cycles between an active GTP-bound and inactive GDP-bound state (PubMed:30723080). In its active state, binds to a variety of effector proteins to regulate cellular responses, such as secretory processes, phagocytose of apoptotic cells and epithelial cell polarization. Regulatory subunit of the phagocyte NADPH oxidase complex that mediates the transfer of electrons from cytosolic NADPH to O2 to produce the superoxide anion (O2(-)) (PubMed:1660188). Activates PLCG2 (PubMed:19394299). {ECO:0000269|PubMed:1660188, ECO:0000269|PubMed:19394299, ECO:0000269|PubMed:30723080}. This is the function of Ensembl gene identifier ENSG00000128340 (RAC2, Rac family small GTPase 2).