Okay, this is from Bulbapedia.
The Lost Zone is an area considered to be a more advanced form of the discard pile. Unlike cards in the discard pile, cards moved to the Lost Zone are kept face-up and are considered to be "outside" the play area due to the fact they are not kept on the playmat if one is used. As such, cards moved to the Lost Zone are no longer considered to be in play, and cannot be retrieved at any time, or by any means, during gameplay.
Is it that hard to search it up on google?