Reveal (公開 Kōkai) is a term that refer to the act of showing one or more cards so that all player is able to see all of their parameter. A card shown in this was is referred to as being "revealed".
Revealing a card does not change its current position or zone, and it stays in revealed state as the effect that revealed the card is being resolved. If there is no specific instruction in the card text, a card in hidden zone is always concealed back after the effect is resolved, and the deck is shuffled if a revealed card is concealed back to the deck.
1005.1 If there is an instruction to "reveal (card)", the parameter of that card is shown to all player.
1005.1a The zone of that card is not changed by this process.
1005.2 When a card in hidden zone is revealed by a card's effect, that card remains in revealed state even if the card's effect is resolved, and if there is no instruction to conceal it in that card's effect, conceal the revealed card. If the hidden zone was deck, shuffle the deck after it was concealed.
Example : "Sakura and Phosflamme, Oath to the Light Wind" is chosen by "Darkness Knight, Yearning K2", if "Sakura and Phosflamme, Oath to the Light Wind" was not played after the deck is shuffled, return "Sakura and Phosflamme, Oath to the Light Wind" to deck, and shuffle the deck