Jaco (also sometimes written as Jako) is an island in the Lesser Sunda Islands. It lies across from the easternmost point of the island of Timor, Kap Cutcha. Its geographical coordinates are 8° 27' S and 127° 20' E.

JACO is a package for the simultaneous modeling of X-ray, Sunyaev-Zel'dovich, Weak Lensing, and dynamical data for clusters of galaxies.