What does ELO mean?

The Elo rating system is a method for calculating the relative skill levels of players in zero-sum games such as chess. It is named after its creator Arpad Elo, a Hungarian-American physics professor.

Amateurs:

<1200         =  Do you know the rules?
1200-1399  =  Beginner
1400-1599  =  Average
1600-1799  =  Above average
1800-1999  =  Strong player

Professionals:

2000-2199  =  Candidate Master (CM)
2200-2399  =  FIDE Master (FM)
2400-2499  =  International Master (IM)
2500+         =  Grandmaster (GM)