The Finger has many meanings and is used in all social settings. As a quick and convenient means of communication, the Finger can be a substitute for a multitude of responses. This simple gesture means anything from "stop taking my picture" or "learn how to drive or I will run you over next time" to "Hi mom, I'm on live television, behind a beat reporter, making you wish I was never born".
The meaning intended usually relates in some manner to an action or dialog from some outside source. In most cases, a person who receives a Finger, either knows the meaning, based on something they have done, or is a blind, stupid, idiot who should be shot into deep space without a spaceship.
The most common excepted meaning of the Finger is “fuck you” ( See fuck you ).
Background: Until the early 1990s, there was no way to communicate 'the Finger' through ASCII. This changed when Slayer invented the MinusZeroEquals symbol to communicate his opinion of most of the users to most of the users of Inferno BBS.
The history of the Finger is hotly debated, but it all comes down to “we don’t know where the hell it came from”. And anybody who says different is full of shit. The history of MinusZeroEquals on the other hand is debated only because I don’t remember the year I invented it. And anyone who says they saw/did/know of it first: -0=