Okay, kiddo, let's talk about Welsh exonyms. An exonym is a name that people who speak a different language use for a place that has a different name in its own language. So if you live in Wales, which is a part of the United Kingdom, you might be used to calling places by their Welsh names. But if someone who doesn't speak Welsh wants to talk about those places, they might use a different name, which is an exonym.
For example, the capital city of Wales is called Caerdydd in Welsh. But in English, most people call it Cardiff. That's an exonym. Another example is the town of Aberystwyth in Welsh. In English, people sometimes call it Aber.
Exonyms can be tricky because sometimes they don't make sense. For example, the town of Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch is located in Wales. It has a very long name in Welsh, but in English, people usually just call it Llanfairpwll or Llanfair PG for short.
So next time you hear someone talking about a place in Wales and they use a name you've never heard before, it might be because they're using an exonym - a different name that people who speak a different language use for that place.