Sacrifice is an order from a player, like order of attacking or order of using Skill, which can only target a card that that player owns. When a card is Sacrificed, that card is sent to the Shrine.
An example of a Seal that has a Skill to Sacrifice a card is Blaze Sage, the Viceroy of Zalom.
Interesting Facts about SacrificeEdit
1. You cannot Sacrifice an opponent's Seal that gets Charm Curse from your card effect (You are not that Seal's owner).
2. You cannot make a card cancels Sacrifice (Sacrifice is an order, not an effect).