USCF and FIDE are different organizations that provide ratings.
USCF is the United States Chess Federation and it provides a rating, FIDE is the international governing body and it uses a very similar formula but because the pool of players is different, the ratings aren't the same. Its the same way that your rating on here would be different than a USCF rating. In general a USCF rating is about 100 points higher than FIDE (not always but about the average). ELO is actually the last name of the guy who invented the system that they use to rate players and is a general term (although ELO is used a lot referring to FIDE ratings). Both of these are official, but depending on where you are playing they may use one rating or the other.
Lastly, different countries have different rating systems and while many of them are similar the ratings differ from organization to organization. Hope this helps and if anyone has more information please feel free to correct me or add to this.
Hi,
What is the different between USCF, FIDE, and ELO ratings? Are they all "official" and if I have a USCF rating, will it be the same as an Fide rating? What are they, in general? Thanks - I'm new to the "real" chess tournament system.