For those who aren’t familiar with motorcycle terms, low side is when the bike basically slides out from underneath you, and you and the bike both go sliding down the road with the bike out in front of you. A high side is when the bike starts to slide out from under you, but then the tires get some momentary grip, and instead of sliding, the bike flips over and launches you through the air in a fairly dramatic fashion.
Example of a high side crash during a motorcycle race:
