In a RaceGorilla competition, a race can be seen as a start-group. In general the start groups are the same as the categories.
Most of the time, a race can be found on the program of your competition.

For example:

Start 10k run 12:00 (this is a race)
Start 5k run 12:15 (this is the second race)

If you competition has one serie with one category and one run, you will have one race.

More about races can be found in the Competition Structure Tutorial.