1) ER=PR=SR:- This all are meant to maintain drug concentration withing the therapeutic window for maximum or desirable period of time.
2) Pulsatile Release: is another type of Controlled release formulation.
(1) and (2) controls only rate of release so they are collectively some time called as "Modified Release" formulations.
3) Delay Release-(ex: Enteric Coated OR colon targeted tablet) is also a Controlled Release formulation but it only controls only site.
Floating Tablet is (as per my knowledge) best example of CR as it target site (stomach) and also controls rate of drug release.
However, some times by some authors, CR , ER, PR, & SR are used interchangeably for the same purpose, i.e. Sustained release.