Okay kiddo, so you know how sometimes when you're playing outside and riding your bike, you might come across a path or trail that's only wide enough for one person to ride their bike on at a time? That's kind of like what single track is for mountain biking.
Single track is a type of trail that's usually narrow and twisty, with lots of curves and bumps that make it fun and challenging for people who like to ride their bikes in the mountains. Because it's so narrow, it's only big enough for one bike to go through at a time, which means that you have to be really careful and pay attention to what you're doing while you're riding.
When you ride on single track, it's important to be safe and follow some specific rules. You should always wear a helmet to protect your head, and try to keep a safe distance from other riders so you don't bump into them. You should also be careful not to ride off the trail, because that can hurt the plants and animals that live there.
Overall, riding on single track can be a lot of fun and a great way to explore the mountains on your bike. Just remember to be safe and respectful, and use your best judgement while you're out there having fun!