What is an assist?

In my research tonite I have found that the NBA RuleBook makes no mention of what an assist is. The NBA’s official statistician manual does though. From what I read, it defines an assist as:

"....an assist is credited to the player tossing the last pass leading directly to a field goal, if and only if the player scoring the goal responds by demonstrating immediate reaction toward the basket...."

From a post on Yahoo!Sports groups one guy explained:

“The statistician manual describes a number of examples as to what is and what is not an assist, with the key point being that if "...continuity.." is not broken then an assist should be credited to the passer. It uses examples like in the case when a pass is made to a player who in the flow of the play then dribbles once, shoots, and scores, then the passer should be credited with an assist. but if the player receiving the pass dribbles more than once, stops, fakes, then shoots and scores, no assist should be credited "...because continuity was broken by the receiver's action to get position on the opponent"....

“Other examples stress if the pass leads directly to a score, then credit an assist, like a pass on a fast break that gets the ball to a player ahead of the pack who then scores, regardless of how many dribbles he takes...

“The key point is if the pass in and by itself puts the receiving player in a position to score, and he then does so in the flow of the play, an assist should be credited. I've sat courtside with statisticians and have been told it’s easily the toughest stat to account for correctly and that many who do so have their "own ways" of crediting an assist...”