I was informed by a long time user (Grumpy Mike) of the Arduino forums when I first started posting there that one should -always- explain the first usage of an acronym or similar construct before using it elsewhere in the rest of a comment.

It makes sense from the perspective of the fact that not all users may understand what the acronym means at first, and doing this is a great courtesy (also, it removes ambiguity in instances where you may be using an acronym similar or same as that for another domain - perhaps the domain of the forum or medium you are communicating on).