Noun
(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.orgBlackjack games almost always provide a side bet called insurance, which may be played when dealer's upcard is an ace. Source: Internet
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. Source: Internet
On the first turn of the round, the non-dealing player has first option of taking the upcard on the discard pile or passing. Source: Internet
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. Source: Internet
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. Source: Internet