RC= Release Candidate..... After a custom ROM goes through extensive testing "beta builds" once they find it completely stable for everyday use they put it into Release Candidate stage. From there they continue to work on different tweaks but usually the "core OS" is completely stable and no longer modified or changed.
AOKP= Android Open Kang Project.... A custom ROM build on AOSP " Ice Cream Sandwich 4.x " source and uses various tweaks and mods from CM team and contributions from many developers.