Nerf

Nerf is a recent term used to describe the altering of a card's effect or ruling, or of the banned/restricted list, to make that card or a certain deck far less powerful or more situational than it used to be. For instance, the card Card of Sanctity, in the anime, was given the effect of allowing both players to draw until they had six cards in their hand. When it was printed as a real-world card, however, that effect was changed to the card's controller removing all cards in their hand and on their side of the field from play to draw two cards. Since the card was so drastically changed in effect to make it far less powerful and - therefore - less desireable, a player may see fit to call it 'nerfed'.

Another example is the card Major Riot; originally, its effect would activate whenever a monster was returned to its controller's hand, regardless of how it was returned. Recent rulings, however, changed it so that the monster must be returned by the effect of the opponent's effect before Major Riot can activate; since the change in ruling severely reduced the amount of combos that can be used with it, it can be considered 'nerfed'.

A final example would be a recent change to the banned/restricted list to limit Thousand-Eyes Restrict, Metamorphosis, and Scapegoat to curb the use of Goat Control. Since many players did not see the reason for limiting all three cards (and, later, banning Thousand-Eyes Restrict without altering the other two cards' status), the deck these limits were supposed to curb was considered 'nerfed', as the major use of the deck was greatly weakened and later nullified, undermining the entire point to the deck, in the first place.