To second Peckish's comments -- terminology differs with manufacturer, time and place...
For me a "charm" is when you use all different fabrics in a quilt regardless of size or shape, not a 5" square, which some refer to as nickels.
Back around Y2K there weren't that many precuts, and certainly no 10" squares or layer cakes. I was part of a fabric swapping group that settled on 10" squares for a bug swap, as that size could be used by all of us and cut conveniently and the concept rapidly spread. For a mental image, that's a 10" width of fabric basically cut into 4 parts. Some fabrics can barely get 40" between the selvedges, and some have a bit left over.
Again, back around Y2K there weren't any established names for 2.5" squares -- other than 2.5" square! Mini-charm or candy or whatever simply was not used when we were trying to get our 2k charm squares.
A "fat quarter" is a yard of fabric cut in half both ways, roughly 18x22ish. A quarter yard is a 9" strip... so is skinny compared to a fat quarter although both are roughly the same amount of fabric.