LOL, or lol, is an initialism for laughing out loud and a popular element of Internet slang. It was first used almost exclusively on Usenet, but has since become widespread in other forms of computer-mediated communication and even face-to-face communication. It is one of many initialisms for expressing bodily reactions, in particular laughter, as text, including initialisms for more emphatic expressions of laughter such as LMAO ("laughing my ass off") and ROFL or ROTFL ("rolling on the floor laughing").

The list of acronyms "grows by the month" (said Peter Hershock in 2003), and they are collected along with emoticons and smileys into folk dictionaries that are circulated informally amongst users of Usenet, IRC, and other forms of (textual) computer-mediated communication. These initialisms are controversial, and several authors recommend against their use, either in general or in specific contexts such as business communications.

The Oxford English Dictionary first listed LOL in March 2011.