In AE, a porch is apparently just about the same structure as a veranda, i.e. an open or enclosed gallery or room attached to the outside of a building.
Besides, a porch (or veranda) can apparently also be designated in some parts of the U.S. alternately as a "(sun) deck", a "gallery", "a "lanai", a "terrace", and a "piazza".
Are any of these regional usages widespread enough to have gotten to flood into mainstream AE?
Also — in dialectal AE — can a large outback or outfront balcony, i.e. a platform that projects from the wall of a building and is surrounded by a railing, a balustrade, or a parapet (like of those found attached to hotel suites, or serving as restaurant dining area) be referred to alternately as a "terrace", a "gallery", and a "patio"?
Best Answer
As a native Mid-Atlantic English speaker, here is how I distinguish them:
A porch is in front of a door, usually a front door. It usually runs narrowly along the front of the house. If you say "back porch," I'll assume it's a small porch in front of the back door, smaller than a deck or patio.
A deck is a wooden structure, usually large enough to spend time and socialize on. It's usually on the back of a house, at ground level or a few feet above. You could call this a "sun deck," I suppose, but it would sound strange to my ears. Just "deck."
A patio is like a deck, but it's made of stone or concrete and may be a short distance away from the house.
A balcony projects out from a building on a floor above the ground floor. At a pinch, a large wooden balcony might be called a deck, but never a patio or porch or gallery.
A gallery is similar to a balcony, but instead of being ouside a building, is inside a large indoor space, like a theater or atrium. This is a much less common word.
Lanai, terrace, and piazza are not idiomatic in my dialect, at least. If you said you had drinks on the lanai, I'd assume you were in Hawaii. If you said you had drinks on the terrace, I'd assume you were in England. If you said you had drinks on the piazza, I'd assume you were in Italy. Ditto with "veranda" and the American South.