A term similar to LOL. It is the silent version meaning "laughing inside loudly" as if one were at church or in public, and you have to keep it inside. It's used in chatting or texting. LinL
The term was made up from seeing people use LOL so much in their texts and chats. The creator wanted to have an acronym for when he wasn't really laughing loudly on the outside because he did want to wake up his neighbors during his middle of the night chats.
Snikering over a joke someone texted you at work, but you don't want to let others know that you are laughing so loudly inside, LinL.
This is the point where a relatively serious person suddenly goes over the edge to a laughing person. It can be brought on by a joke or a situation, and it doesn't require any prompting although previous jokes increase the chance of breaking the laugh limit.
John was being very serious about his financial situation until he saw a very funny political video, and then suddenly he broke the laugh limit. Then he was laughing so hard that he almost cried.