The term "jodphurs" or "jods" is more common in the UK, but still heard in the US. But what's the etymology?
It's all the fault of the British and their love of polo. In 1897, Queen Victoria invited a number of people to her Diamond Jubilee. One of them was the younger son of the Maharaja of Jodphur, a man named Pratap Singh.
He brought his entire polo team with him and proceeded to kick some serious butt and defeat most of the British teams. He also brought the style of riding trousers popular in Jodphur.
The English combined the style with their traditional riding breeches to create modern jodphurs. In the US, "jodphurs" and "breeches" are used interchangeably, but technically they're breeches if they end just below the knee and are worn with tall boots and jodphurs if they go all the way down to the ankle and are worn with short riding boots (called paddock boots in the US and, you guessed it, jodphur boots in the UK).
Jodphurs can be worn with tall boots or chaps as well.