What is bracket racing?

Wikipedia: 

Bracket racing is a form of drag racing that allows for a handicap between predicted elapsed time of the two cars over a standard distance, typically within the three standard distances (1/8 mile, 1,000 foot, or 1/4 mile) of drag racing.
 

https://en.wikipedia.org/wiki/Bracket_racing

 You can also check out Michael Beard's Guide to Bracket Racing.