What does x000 mean in yu gi oh?

Answer 1

Slifer The Sky Dragon has X000 ATK:

Slifer the Sky Dragon

DIVINE/Divine Beast/10/?/?

You must offer 3 Tributes to Special Summon this card. The ATK and DEF of this card becomes the number of cards in your hand × 1000. When this card is Special Summoned from the graveyard, it is sent to the Graveyard during the End Phase. While this card is face-up on the field, it cannot be targeted by Spells, Traps, or Monsters that designate a target. Additionally, when your opponent successfully Summons a monster 2000 points is deducted from the Monsters ATK or DEF respective to its position. If this effect reduces the amount to 0 or less the monster is destroyed.