Discard

Discard refers to a card being sent from the hand to the Graveyard as either a cost or the result of a card effect. It is important to know that a card is not considered discarded unless the effect that causes it to be sent to the Graveyard specifically says "discard".

There are 3 reasons a player would discard a card.
 * The discard is a cost for an effect. Activating Lightning Vortex requires that you discard 1 card to activate it.
 * The discard is a result of an effect. Being attacked directly by X-Saber Airbellum forces you to discard a card.
 * There are more than 6 cards in a player's hand during their End Phase. The turn player must discard until they are holding 6 cards.