Lancet Window: A Tall, narrow window with a pointed-arch top, characteristic of Gothic architecture, and often with leaded diamond shaped lights.

Latch: device on the interior face of the sash that retains the window sash in place.  It also allow the sash tilt in for easy cleaning.

Light or lite: Glazing framed by muntins and/or sash in a window or door.

Lift rail: A handle or grip installed on the bottom of the lower sash rail of a double-hung window to make it easier to raise or lower the sash.

Low-E Glass: Glass that has a coating with low emissivity that restricts the passage of radiant heat and UV light for better energy efficiency and protection from fading.