Clerestory

Cambridge Dictionary draws the line at head height. On that definition a clerestory is a part of a wall, and what makes it one is where its windows sit: above the height of the people in the room, not at the level a person standing there looks through. A skylight set in a roof is not one, because it is not in a wall.

The test follows from those words. Ask where the glass sits, not how large it is. A band of windows set high in a wall, above anyone's head, fits the definition. A tall window that starts at eye level and runs up past head height is harder to call on the wording alone, because much of its glass sits where people look through it.

A related but different piece of glass, the small window set over a door, is a transom, and the two words are not interchangeable even though both sit above the usual sightline.

Exterior glass set that high is cleaned by the trade's published methods. NGA's procedure for exterior glass begins at the top of the building and continues to the lower levels, to reduce the risk of leaving residue and cleaning solution on glass already cleaned, and it includes checking that the wind is not blowing solution and residue onto cleaned glass.

NGA's paper also records a second technique, one IWCA recognizes and some professional window cleaning contractors use, in which the rinse water is generally allowed to evaporate. It is covered on the service page at pure water and the water-fed pole. A definition does not settle which of the two methods suits a given band of high glass.

A ladder set against the house is its own question with its own rules, at whether window cleaners use ladders, and glass reached without one is answered at second-story windows cleaned from the ground. Divided panes in the windows below a clerestory, where a house has them, are their own term: muntins.