Busting cards means are cards that the dealer shows, which may have the effect of bringing him over 21 on a hit. The dealer’s hole card is a 10 value, then busting cards have values of 4, 5 or 6. 7, for instance, couldn’t be a blackjack busting card since if the dealer has a 10-value card hidden.
We can never be quite sure what card the dealer is hiding, and so this is where basic strategy comes in. Busting cards make up a part of the basic blackjack strategy since the decision whether to hit or stand is front and center when looking at the dealer’s card.
If are holding a hand that totals 12, since you’ve got a pretty low hand and are quite a way from 21, but look carefully at the dealer’s hand. If they’re holding any of the busting cards (4, 5, or 6) then there’s a very good mathematical chance of them busting on a hit, so rather than hit on your 12 hand, you take proper advantage of the odds and stand.
Just remember that your best play is always with the odds, so don’t give up, take heart, and watch for those busting cards.