drop-head window
A double-hung window whose lower sash can drop through the window sill into a pocket below the sill.
Glossary
double-hung window
Glossary
cottage window
A double-hung window having its upper sash smaller than the lower sash; the upper pane is often decorated.
Glossary
cased frame, boxed frame, box frame
The wood frame of a double-hung window; has hollow jambs or mullions which contain the sash counterweights
General
box mullion
The built-up mullion of a cased frame of a double-hung window; has hollow jambs containing the counterweights.