(quick guide & examples)
The number of ways we can arrange a list of things.
The order in which it is arranged does matter.
A, B, C, AB, BC, etc... are not permutations of "ABC".
Permutation is "number of ways to arrange a list", not "number of variations".
The number of ways we can create from a list of things.
The order in which it is arranged does not matter.
* The order does not matter. So BA=AB, CA=AC, BC=CB, CAB = ACB = BAC, etc...