A stone-cold bluff is a form of bluff that leaves you with little chance of improving if players decide to call your bet or raise, which occurs frequently in micro-stakes poker games.
Of course, this is very different to semi-bluffing, because even if called, could lead to big payoffs if the turn and river fall your way.
So keep your bluffing to semi-bluffs at the low-limit tables, and you will do fine. Most novice players bluff with no outs and chance of winning the pot far too often.
EXAMPLE “When involved in a hand against multiple opponents, I don’t like to make a stone-cold bluff, because I can’t expect to get many folds.”