Methine

In chemistry, methine (also known as methylidyne) is a tri-valent functional group CH, derived formally from methane. The methine group consists of a carbon atom bound by two single bonds and one double bond, where one of the single bonds is to a hydrogen.

It is sometimes used non-systematically for a carbon with four single bonds, where one bond is to a hydrogen.

Example
Every carbon in this molecule is a methine carbon, except the two attached to the two nitrogens and that are not attached to any hydrogens. There is a five carbon poly-methine chain in the center of this molecule.