A comment is a piece of code that is not run by the computer. In Java, it is started with a //. <syntaxhighlighting lang="java"> // This is a comment // This will not be run. </syntaxhighlighting>

A multi-line comment is started with a /*, and ended with a */. <syntaxhighlighting lang="java"> /* This is a multi-line comment. I will not be run either. </syntaxhighlighting>