There are official constellations, and then there are other shapes/patterns known as asterisms. This article will be able to explain way better than I could in a reply here.
It seems like the important thing about the 88 officially-enumerated constellations is that they divide the sky up into standardized sectors. Asterisms are just the stars themselves.
In other words, the asterism "The Big Dipper" is exactly seven stars. Since these stars are prominent, they--and some others--define the constellation "Ursa Major" but the constellation is actually the region of space around them. Thus, you could say that you can see (e.g.,) a comet "in" Ursa Major, but not "in" the Big Dipper.
https://www.skyatnightmagazine.com/advice/constellations-ast...