Okay kiddo, imagine you're riding a bike and you're going around a turn really fast. Suddenly, you lose control of the bike and it falls over onto its side. That's a lowsider.
In simple terms, a lowsider is when a motorcycle or bike loses traction in a turn and falls over onto its side. It can happen when someone is going too fast, takes a turn too sharp, or hits a slippery patch on the road.
It's not a fun experience for the rider, as they can get hurt pretty badly when they hit the ground. So it's always important to drive safely and be aware of the road conditions around you.