The void operator evaluates an expression and then returns undefined, regardless of the expression's result. For example, void(2 + 2) evaluates 2 + 2 (which is 4) but returns undefined. One common historical use was in HTML links to execute JavaScript without navigating: <a href="javascript:void(0)" onclick="myFunction()">Click me</a>. In modern JavaScript, it's less commonly used, but it can be a concise way to get undefined (void 0 is shorter than undefined and can't be overwritten).