Where Did Chomping at the Bit Originate?

This phrase (or idiom) comes from the sport of kings: horse racing. A bit is part of the apparatus that goes in the horse's mouth and connects to the bridle and reins so the horse can be controlled and directed by the jockey on its back.

What does chomping at the bit mean?

: waiting in an impatient way to do something We've all been champing at the bit to get started on the project. The team was chomping at the bit for their chance to play the defending champions.

Is the phrase chomping at the bit or champing at the bit?

The original phrase is, indeed, champing at the bit, but chomping at the bit emerged in America in the 1930s according to the Oxford English Dictionary and chomp has overtaken champ in common use. A Google web search for chomping at the bit returns about twice as many results as a search for champing at the bit.