Jamb.  A vertical member at the side of a window or door frame.

Jamb depth: Width of the window frame from inside to outside.

Jamb liner:  The plastic or metal track installed in the jambs of a double hung window in which the window sash slide.

J-Channel: is used to trim out the ends of siding panels where they meet a door or window and to cover cut edges of panels around windows and doors.

Jal-awning window:  a window consisting of a multiplicity of top-hinged sash arranged in a vertical series within a common frame, each operated by its own control device which swings the bottom edges of the sash outward.