>>17
Most mathematicians use 'set' to mean a collection of distinct things (the 'things' can be anything, even unrelated items) where ordering does not matter. You might be confused because in a lot of books on set theory (or books that use set theory), they leave a set as an undefined concept, which sounds nice and formal, but in reality there is an intuitive motivation behind the concept of a set they just assume everyone shares. Hope that helps, if not, feel free to ask.
Also,
IHBT.