Small GTPase which cycles between active GTP-bound and inactive GDP-bound states. In its active state, binds to a variety of effector proteins playing a key role in the regulation of endo-lysosomal trafficking. Governs early-to-late endosomal maturation, microtubule minus-end as well as plus-end directed endosomal migration and positioning, and endosome-lysosome transport through different protein-protein interaction cascades (By similarity). Involved in lipophagy, a cytosolic lipase-independent autophagic pathway (By similarity). GTP + H2O = GDP + H(+) + phosphate Belongs to the small GTPase superfamily. Rab family.