A clathrate, clathrate compound or cage compound is a chemical substance consisting of a lattice of one type of molecule trapping and containing a second type of molecule. The name clathrate complex used to refer only to the inclusion complex of hydroquinone, but recently it has been adopted for many other weak composites which consist of a host molecule (forming the basic frame) and a guest molecule (held in the host molecule by inter-molecular interaction). Clathrates are also called host-guest complexes, inclusion compounds, adducts (chiefly in the case of urea and thiourea) and, in the oil industry, hydrates. They used to be called molecular compounds.

A clathrate hydrate, in particular, is a special type of gas hydrate in which a lattice of water molecules encloses molecules of a trapped gas. Large amounts of methane naturally frozen in this form have been discovered both in permafrost formations and under the ocean sea-bed. Researchers have begun to investigate silicon and germanium clathrates for possible semiconducting and superconducting properties.

The word clathrate is derived from the Latin clatratus meaning with bars or a lattice. Wikipedia