Methylidyne, or (unsubstituted) carbyne, is an organic compound whose molecule consists of a single hydrogen atom bonded to a carbon atom. It is the parent compound of the carbynes, which can be seen as obtained from it by substitution of other functional groups for the hydrogen.
The carbon atom is left with either one or three unpaired electrons (unsatisfied valence bonds), depending on the molecule's excitation state; making it a radical. Accordingly, the chemical formula can be CH or CH  (also written as ⫶CH); each dot representing an unpaired electron.  The corresponding systematic names are methylylidene or hydridocarbon(•), and methanetriyl or hydridocarbon(3•).  However, the formula is often written simply as CH.
Methylidyne is a highly reactive gas, that is quickly destroyed in ordinary conditions but is abundant in the interstellar medium (and was one of the first molecules to be detected there).