One of the most basic mathematical groupings are pairs and couples. A pair is symbolized using the set construct {u, v} while a couple is symbolized using tow parentheses (u, v).

{u, v} is obviously a set of tow elements which give this property {u, v} = {v, u} whatever u and v are.
While (u, v) = (v, u) only and only if v = u.

A direct translation to programming makes (u, v) a tuple in python, while {u, v} can be represented by many abstractions like Set in java.

Knowing this distinction can come in handy when studying graphs or any other mathematical field that relies on the definition of those tow basic elements.