Chafing is when your clothes rub against your skin and a wound develops.
This is a tricky injury to prevent because it can come out of nowhere! Extra warm and/or long runs where you sweat more than usual may increase the chances of chafing. Wearing a running belt for a short run may be fine but wear it for a longer run and it could cause some friction.
The best way to prevent chafing is to be mindful of your gear. Know which shorts are great for long runs and which ones you want to avoid spending 2 hours in. Same for shirts or any other gear.
If you’ve already developed some chafing it’s best to lube it up for a few days so it can heal. Typically this will be adequate and it won’t be an issue again (until you forget to lube up before a long run!)