Discarden betekent dat je een kaart vanuit je hand in de graveyard legt, dus ja, het is altijd vanuit je hand.
Als het vanaf de battlefield naar de graveyard is, hebben we het over "dies", "destroy" of "sacrifice".

En gewoon om even zeker weten duidelijk te zijn, heb ik de officiële definities voor je opgezocht in de Comprehensive Rules:

700.4. The term dies means "is put into a graveyard from the battlefield."

701.6. Destroy
701.6a To destroy a permanent, move it from the battlefield to its owner's graveyard.

701.7. Discard
701.7a To discard a card, move it from its owner's hand to that player's graveyard.

701.14. Sacrifice
701.14a To sacrifice a permanent, its controller moves it from the battlefield directly to its owner's
graveyard. A player can't sacrifice something that isn't a permanent, or something that's a
permanent he or she doesn't control. Sacrificing a permanent doesn't destroy it, so regeneration
or other effects that replace destruction can't affect this action.