Cross country running is a special kind of running that people do on trails, fields, or even through forests! It's called cross country because the runners have to run across different kinds of uneven terrain instead of just running on a regular road or track.
Cross country races usually take place outside and can be pretty far - sometimes two, three and even four miles long! Runners race against each other, but they're also racing against the course itself, trying to beat the challenges in front of them, like hills, mud puddles, and rocky paths.
The people who run cross country races are usually very fit and practice running on different kinds of surfaces so that they can handle whatever the course throws at them. They also wear special shoes that have good grip, so they don't slip and fall when they're running over loose rocks or unpaved paths.
So when you see runners racing through fields and forests, remember that they are doing cross country running and it's a fun way to explore the outdoors while staying active!