The bond between two people that are normally of the opposite sex. Not to be confused withfriends with benefits. The people people may seem like more than friends, but to them, they couldn't ask for more. They love each other more than most friends do, and they would do anything for each other. They hold a special place in each others heart. Most biffles later on end up dating, but they still hold that biffle status.
An idiotic word which shows how the acronym 'BFFL' would be written if it became a proper term, god forbid. It means 'best friends for life', although in most cases this is generally a lie as you often lose contact with friends, especially if they were made when you were young.