Asterism

A recognisable pattern of stars that isn't an official constellation, like the Big Dipper or the Coathanger.

The Big Dipper (the Plough) is part of the constellation Ursa Major; the Summer Triangle spans three constellations; the Coathanger is a little hook of stars in Vulpecula. Asterisms are chance alignments — the stars are usually at very different distances — but they're great signposts for star hopping.