The main frame includes the head, sill, and jambs of a window.

A mechanically fastened frame is fastened with screws instead of other methods.

The meeting rail is the horizontal part of a pair of sashes that meet when the sashes are closed.

The meeting stile is the vertical part of a pair of sashes that meet when they are closed.

Mesh is a fabric made of fiberglass or aluminum used for screens on windows and doors.

When two windows are joined together side by side, they are mulled.

A mullion is a vertical or horizontal connecting unit dividing windows or doors.

A muntin bar is a strip of wood or metal used to divide and hold panes of glass in a window. Also known as a grille or mullion.