The word 'rotations' is being thrown around all the time.
Why is it called "rotations"/"rotating"?
Rotation is a term used in quite a few games, mainly tactically. In terms of Fortnite it means to have a path to follow from one point to another.
For example, if you dropped paradise palms and the circle is centered on dusty divot, you want to get as much gear as possible before getting to the ending circle, so you would change your rotation around this. This means you could start at Paradise Palms -> Retail Row -> Dusty Divot, or if you loot quick enough you could add more locations into your rotation, like Paradise Palms -> Retail Row -> Fatal Fields -> Salty Springs -> Dusty Divot.
In short the term is just a word to use when deciding your path into the end game circles with the objective in mind being to find the most chests/loot on the way there to give you a better chance in the late game.