Metadata publishing is a way for people to provide information about a certain thing or object online. For example, if you published a book, you can provide its title, author's name, number of pages, the date it was published, and other details. Providing this information in a standard way makes it easier for other people to find it and use it. Think of it like having a library catalogue - when you want to find a book, you can take a look at the catalogue and search for the title to see what books the library has. Metadata publishing is the same kind of thing, but online.