When discussing horse racing, to many only one thing comes to mind: The Thoroughbred. There are other forms of racing such as steeple chase and harness racing, but by far the thoroughbred horse race is what gets racing fans excited. The Kentucky Derby isn't called the most exciting two minutes in sports for nothing!
The Kentucky Derby is just one race in what is considered the grand slam of horse racing, The Triple Crown. Race fans far and wide clamber to their sports books, their racetracks, and their television sets to see the best of the best racing in a grueling combination of races that create the Triple Crown. The Kentucky Derby, The Preakness, and The Belmont Stakes make up the most coveted prize in horse racing and to date only 11 horses have achieved such a high level prize.
That said, Stakes races are the highest level of competition in horse racing and usually reserved for the best horses. Owners must pay an entry fee to run their horses in stakes races. This money is added to the prize money awarded to the winner. Stakes races may also be Graded Stakes imparting a certain "level of class" to the race.
All races have certain criteria a horse must meet to race. A horse race may put additional weight requirements on better horses within a race. This is called a Handicap race. The weight carried will be determined by the horses past performances.
Some races may list "non winner of three" as a racing requirement. This is an Allowance race. These thoroughbreds have usually separated themselves from the pack in terms of performance and are being groomed for racing with better horses. Most horses at this level will go on to Handicap and Stakes races.
The most common race is called a Claiming race, this can also be an "Optional" Claiming race. Before the race is run, owners specify an amount that the thoroughbred can be purchased or "claimed" for. This may or may not be advantageous to the owners of a horse. In one respect it levels the racing field; certainly one would never list a better horse for a claimer. However, there are many horses that have been claimed at a race that simply needed better training to become a champion.
Lastly there is Maiden race. This race is exclusively for thoroughbreds who have never won a race. This race is the horse's stepping stone into the other races listed above. It is said that the thoroughbred "broke his maiden" when he finally wins.
All of these races may be combined in a single days racing. Tracks typically have eight or more races in a day. It makes no difference which type of race the fan sees throughout the day, whether they have money bet on a thoroughbred or if they just picked one for fun, nothing breaks a crowd into to as wild, fervent excitement as their horse getting closer and closer to the finish line.