Free card (フリーカード Furī Kādo) is one of the classification of cards in Z/X -Zillions of enemy X- TCG and also one of its main gimmick as a "free-to-start" card game.
Free cards in Z/X TCG are similar to sample decks or freebies in other trading card games. However, one of the main characteristic of free cards in Z/X is that all of them are legal to be used in official tournaments and events. The rarity of all free cards are fixed as Free (F), and they also can be copied and printed for use.
Free cards are usually released as a "trial" or "sample" version for an upcoming sets, with every sets has one or more free sets featuring several free card version of cards from that set that was released before the set itself. Most of them are distributed in various Z/X official shops and events as a "Free Card Booklet" (フリーカード冊子) or available for download in Z/X official website. Some magazines and publications such as V Jump and Card Gamer may also comes with its own free cards.
Compared to their original, commercial cards counterparts, the majority of free cards are usually inferior in terms of Power and/or ability. Some of them might also be vastly different to the original cards, while the others did not have any differences at all (it should be noted, however, that only the free card version can be copied and printed for use in this case). One of the striking differences between a free card and its original card counterpart other than its stats and/or rarity is that the free card version doesn't feature any background in its artwork.
From "Magical Beast of Prominence & Revenant of Darkness" onward, most of the newer free cards are released with time-limited ability (e.g. "This ability is available until..."). This makes them almost similar to their original counterpart, but with the drawback of making the ability unavailable for use after the time period is over.
Since free cards can be mixed with the generic, commercial cards, it is advised to put them all inside card sleeves with opaque backing so as not to accidentally marking the cards.
For the list of all cards that also available as free card, see Category:Free Cards.