Blackjack glossary: every term, defined.
Quick definitions for the jargon you'll see on the felt, in rule books, and across the rest of this site. Anchor links to share a specific term.
A
Ace
#- Worth 1 or 11, whichever helps the hand more. Aces are why blackjack has “soft” totals. A hand with a usable ace can't bust on one draw.
B
Basic strategy
#- The mathematically optimal play for every hand vs. every dealer upcard, assuming no information about future cards. The whole chart lives at /strategy.
Bet spread
#- The ratio between your minimum and maximum bet. Counters spread bets to capture EV when the count is positive. A 1:8 spread is roughly the maximum a casino will tolerate before back-offs.
Blackjack
#- An ace plus any ten-value card on the first two cards: an unbeatable 21 on the deal. Paid 3:2 at good tables, 6:5 at bad ones.
Bust
#- Going over 21. Bust = automatic loss, even if the dealer also busts afterwards (you act first).
C
Continuous shuffle machine (CSM)
#- A machine that returns played cards to the shoe and reshuffles after every round. Eliminates deck depth and makes counting impossible.
D
DAS (Double after split)
#- Rule allowing you to double down on a hand created by splitting a pair. Worth ~0.14% to the player and changes a handful of pair-split cells on the chart.
Deviation
#- A play that departs from basic strategy because the count makes a different action higher EV. See the Illustrious 18 for the headline deviations.
Double down
#- Double your bet, draw exactly one more card, and automatically stand. Available on your first two cards. Some tables restrict doubles to totals 9–11 or 10–11.
E
EV (Expected value)
#- The average outcome of a decision over infinite trials. Expressed as a fraction of your bet (e.g., +0.5 EV on a $10 wager averages $5 to the player long-run).
H
Hard hand
#- A hand with no usable ace (or an ace forced to count as 1 to avoid a bust). Hard hands can bust on a single draw.
Hit
#- Take another card.
H17
#- Rule variant where the dealer must hit a soft 17. Costs the player ~0.22% vs. S17. See house edge by rule.
Hole card
#- The dealer's face-down card. Revealed when the dealer plays. Knowing the hole card via dealer error or angle-shooting is called hole carding and is technically not card counting.
I
Illustrious 18
#- Don Schlesinger's shortlist of the 18 count-based deviations from basic strategy that capture most of the EV from a Hi-Lo count. See /counting.
Insurance
#- Side bet offered when the dealer shows an ace, paying 2:1 if the hole card is a ten. A losing bet under basic strategy; counters take it only at true count ≥ +3.
K
KO (Knockout count)
#- Unbalanced counting system: 2–7 = +1, 8–9 = 0, 10–A = −1. Skips the true-count division. Bet decisions key off the running count directly. Simpler than Hi-Lo, slightly less precise.
L
Late surrender
#- Surrender option that's offered after the dealer peeks for blackjack. The standard variant when surrender is available.
N
Natural
#- Synonym for a two-card blackjack: an ace + a ten on the deal.
P
Peek
#- Procedure where the dealer checks the hole card for blackjack when showing an ace or ten. Prevents you from losing extra money on doubles and splits to an unrevealed blackjack.
Penetration
#- How deep into the shoe the dealer plays before reshuffling, usually expressed as a percentage. Deeper penetration = bigger edge for counters. 75–80% is decent; 50% is a waste.
Push
#- A tie between your total and the dealer's. Bet returned.
R
RSA (Resplit aces)
#- Rule allowing aces from an initial split to be split again if you draw another ace. Worth ~0.07% to the player. Rare.
Running count
#- The cumulative tally of card tags since the last shuffle. Convert to true count by dividing by decks remaining (for balanced systems like Hi-Lo).
S
S17
#- Rule variant where the dealer must stand on all 17s, including soft 17. The player-friendly default. Compare with H17.
Shoe
#- The physical box that holds the multi-deck stack the dealer draws from. Modern blackjack typically uses 6 or 8 decks per shoe.
Soft hand
#- A hand with an ace counted as 11. Can't bust on one draw. The ace silently drops to 1 if the next card would otherwise bust you.
Split
#- When dealt a pair, separate the two cards into two hands, each receiving a fresh second card and an equal bet. See splitting aces and splitting 8s.
Stand
#- Keep your current total and end your turn.
Stiff
#- A hand total that can bust on a single hit, usually 12 through 16. The hands that make blackjack decisions hardest.
T
U
Upcard
#- The dealer's face-up card. It's the variable that drives most basic-strategy decisions. Weak upcards (2–6) call for defensive play; strong upcards (7–A) call for aggressive play.