Blackjack - Advanced Strategy

Because basic strategy is based on a player's point total, and the dealer's visible card, basic strategy plays can often be incorrect. This is because a player may achieve different point totals with different cards, and a different number of cards. A more complete strategy would require a much more complex table, which is why the table above is named 'basic.'

Advanced strategies take into account a player's hand composition (number of cards and their individual values). For example, the basic strategy is to hit a total of 16 against a dealer 10 card. However if a player's total of 16 contains a 4 or a 5 card (such as a three card hand of 9 5 2), the correct stategy is actually to stand. Another example is a player's total of 12 against a dealer 4. Basic strategy says to stand, but if the player's total of 12 contains a 10 card (such as 10 2) then the correct action is actually to hit.

Advanced strategy can also include information from other players' hands. For example, if you have 10 3 and the dealer is showing a 2, the correct strategy is to stand, even with the ten you do have. But if other players are showing many tens, the correct strategy may actually be to hit. These slight variations in play help reduce the house edge.

From Wikipedia's