Imagine you have a puzzle with different shaped pieces, but only certain pieces fit together correctly. When you try to put a wrong piece in a spot, it won't fit and you'll know it's not the right one.
XML validation is like that! It's a process that checks if the XML data you have is correct, like a puzzle piece that fits where it should.
A computer program or system checks the XML data to make sure it follows specific rules or requirements called a schema. Just like in a puzzle, the computer knows when a piece doesn't fit correctly, it can also tell when the XML data doesn't follow the schema's rules.
If the XML data passed the validation, then it's considered valid and can be used without any problems. If it doesn't pass, you'll have to check which parts are incorrect and fix them so the data can be used correctly.
So to sum it up, XML validation is like checking puzzles and making sure everything fits in the right place. A computer program checks the XML data to ensure it follows specific rules or requirements, and if everything's correct, the data can be used without any problems.