Fanlight – Smaller opening section found at the top of the window.

Window frame – Collective term used to describe the head along the top of the window, the cill along the bottom and the two vertical jambs.

Casement – The opening part of the window, in which the glass sits.

Head – Also known as first mullion. The horizontal bar across the top of the window frame.

Top Rail – Horizontal bar across the top of the casement.

Bottom Rail – The larger horizontal bar across the bottom of the casement.

Stile – The vertical edges of a casement.

Jamb – The two vertical sections on the outer edge on each side of the window frame.

Cill or sill – Horizontal across the bottom of the window frame.

Mullion – Vertical bar within the frame and separates two casements.

Transom – Horizontal bar that separates two casements.

Direct glaze – Where the aperture for a casement is directly glazed with glass without a casement.