In light-frame construction, a trimmer is a timber or metal beam (joist) used to create an opening around a stairwell, skylight, chimney, and the like. Trimmers are installed parallel to floor or ceiling joists and support perpendicular headers.

It can also refer to a jack stud

Wall stud

A wall stud is a vertical member in the light frame construction techniques called balloon framing and platform framing of a building's wall.-Purpose:...

 that supports a header above a window or door opening.

Traditionally, a stud which was less than full length was sometimes referred to as a cripple

Cripple

A cripple is a person or animal with a physical disability, particularly one who is unable to walk because of an injury or illness. The word was recorded as early as 950 AD, and derives from the Proto-Germanic krupilaz...

.