Galinstan is a brand name for an alloy composed of gallium, indium, and tin which melts at −19 °C (−2 °F) and is thus liquid at room temperature. In scientific literature, galinstan is also used to denote the eutectic alloy of gallium, indium, and tin, which melts at around +11 °C (52 °F). The commercial product Galinstan is not a eutectic alloy, but a near eutectic alloy. Additionally, it likely has added flux to improve flowability, to reduce melting temperature, and to reduce surface tension.

Gallium is a chemical element; it has symbol Ga and atomic number 31. Discovered by the French chemist Paul-Émile Lecoq de Boisbaudran in 1875, gallium is in group 13 of the periodic table and is similar to the other metals of the group.