An XML editor is a piece of software that is used to modify files written in the XML programming language. XML is short for eXtensible Markup Language, and is used to structure data, like the contents of a webpage, in a way that's easy for computers to read. XML editors make it easier to work with this type of data by providing features like color-coded text, a preview window, search and replace functions, and auto-completion. These features allow you to quickly edit, read, and understand XML data.