Elfreth’s Alley is a small street in Philadelphia commonly known as America’s oldest residential street. I don’ think we know exactly when it first was built up, but there seems to be a consensus that it goes back to the early 1700s.  This is a of a passageway between two buildings on the alley. In New York, most people would call this space between two buildings an alley. But calling the post Elfreth’s Alley Alley seemed a bit contrived. Looking for an alternative word I discovered this page where the issue is actually discussed (the Internet seemingly has a page for almost everything). It seems this would be called a gangway in Chicago, but not anywhere else.