It's original definition was "Laughing out loud" (also written occasionally as "Lots of Laughs"), used as a brief acronym to denote great amusement in chat conversations.
Now, it is overused to the point where nobody laughs out loud when they say it. In fact, they probably don't even give a shit about what you just wrote. More accurately, the acronym "lol" should be redefined as "Lack of laughter."
A: I'm probably gonna kill myself tonight...
“One day, someone showed me a glass of water that was half full. And he said, "Is it half full or half empty?" So I drank the water. No more problem.” --Alexander
A term commonly used on the internet when you're not really paying attention, or have nothing to say.
Person: Man, my grandma died today. I'm totally bummed.
Person: Today was boring.
*10 minutes later*
Stolen from someone ;-)
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Originally defined to mean "laugh out loud" but is now so overused that no one is actually laughing when they type it. It is just something that people say when they have nothing else left to say. Often the words "hahaha" are substituted for it to give variety. People also type emoticons such as: ":]" to also fill in the space when they get tired of "laughing out loud" or not "laughing out loud". It is the most used word when texting, and one of the easiest to type in order to send a message to someone so that you don't look like your blowing them off.
Person 1: "Hey man, what's up?"
Person 2: "Not much, what about you?"
Person 1: "Yeah same here."
Person 2: "lol"
Person 1: "haha :]"
Person 2: "lol"