An abbreviation for "Laugh Out Loud" that is used in cyberspace. It is rarely (if ever) meant literally. Maybe there was a time that it LITERALLY meant "Laugh Out Loud", however, I have been active in cyberspace for over ten years and am unaware of this time.
What “lol” is, is simply an ‘online lingo’ that is used to communicate things that IRL
(in real life) would otherwise be communicated through tone of voice, facial expressions or body language. In particular, “lol” is used to signify that the individual typing it finds something humorous about what they are saying EVEN IF this individual typing it may not literally be "laughing out loud”
"lol" and most other 'online lingo' also tend to be used in text messages and high school note-passing. And with the exception of text messages (when laziness may ensue), the first letter to “lol” is not usually capitalized, even when it is the start of a sentence or a sentence by itself.