upcard
Noun
Meaning
(card games) In stud poker or blackjack, a playing card dealt face up and left on the table for others to see.
(card games) In rummy, the top card of the discard pile.
Source: en.wiktionary.orgExamples
Blackjack games almost always provide a side bet called insurance, which may be played when dealer's upcard is an ace.
Depending on the rules, a card that is accidentally dealt face up or otherwise revealed may become an upcard, or may be discarded, or may invalidate the entire hand.
On the first turn of the round, the non-dealing player has first option of taking the upcard on the discard pile or passing.
So if the first upcard is a 4, you can knock and go out with only 4 or fewer points in your hand; and if the 4 was a spade, you would get double points that hand.
If the non-dealing player takes the upcard, the player acting second can take the top card from the pile of his or her choice.