A rating is a number which indicates, based on your past performance, how good you are at chess. The higher the number the better you are.
As at April 2012 the highest rated player in the world was Magnus Carlsen with a rating of 2835. You can see the highest rated players in the world on the FIDE top players list
The highest rating ever was Garry Kasparov reaching 2849 in July 2000.
The best players in the world have ratings as follows:
World Champion 2800
International Master 2400
National Master 2300
For juniors in New Zealand the easy way to gauge if you are on track to becoming a Champion is to take your age and multiply by 100
Eg. Age 9, good target to have a rating in the 900's
Age x 100 = You should be playing in Regional Championships
Age x 100 (+100) = You will qualify for National Championships
Age x 100 (+200) = You may be selected to play in a World Championships This formula only works for juniors (until age 18). How does my rating compare with other Ratings; eg FIDE (International) Rating?
The ratings are calculated using the same scale as international ratings. See FIDE ratings
There are lots of different ratings. Many websites have their own rating system. Some chess clubs or associations have a ratings system. All of them try to maintain their systems as being comparable to the FIDE system. With each system there will be some variation, but good system administrators try to keep this variation from FIDE ratings to a minimum.The Technical Stuff
The ratings formula used for FIDE can be found in the FIDE handbook