What is the different between @This() and struct?

Hello, guys. So I starting to learn and read zig codebase in github/codeberg. I notice some of the projects/codebase use @This() with PascalCase.zig filenames and some of them are using struct with lowercase.zig filenames. Is there any difference using @This() and struct? Sorry, if some of you don’t understand my questions. My English is not good and I’m still learning programming. Thanks.