back alley

plural back alleys

1. An alleyway that runs behind a row of houses, or between rows of houses.

   Near-synonym: bylane

   1 more example

   Apocalypse also happens to be a Fagin figure, shuffling around the back alleys of Cairo, where he makes the weather-controlling pickpocket Storm (Alexandra Shipp) his first follower by offering her baubles.

   2016 May 23, Ignatiy Vishnevetsky, “Apocalypse pits the strengths of the X-Men series against the weaknesses”, in The Onion AV Club

   Synonyms: back lane, backway, bylane

2. euphemisticslangThe anus.

   RALPH: This dress is not made for a big boy. It's going right up the back alley there.

   2018, Ralph Breaks the Internet (film)

   1 more example

   Nobody goes up my back alley without a rubber on and I don't do heroin, so what's the worry?

   1991, Mack Tanner, The Stalker, page 178