This usually refers to the combination of a top of some kind, and side and back curtains, which would fully enclose the aft cockpit area. The top can be hard, (built as part of the boat), or soft (canvas top on a frame). The enclosure panels may have lots of windows, no windows (fabric only), or something in-between, (perhaps a medium sized window in the back section only). Careful consideration should be given to the typical use of the boat when deciding how much window to include.