they're the messages at the top of each board, e.g. the ones at the top of this board(see attachment).
They're called "stickies" because they're "stuck" at the top of the board and can only be moved down on to the next page if a mod "unstickies" them.
They have been "stuck" because they're either useful or important and it is recommended that you read the stickies at the top of each board before posting on that board
hope you understand this, cos stickies are usually important(see the sig size one)
Part of solving the problem is actually noticing that the problem is there in the first place