Mint in sealed box

From Brickwiki

Mint In Sealed Box (MISB) is a term used by collectors and sellers to denote a set that has never been opened. The packaging itself may not be in pristine condition, but everything should be present on the outside (still shrinkwrapped, if, as for earlier sets, it came that way) and all package seals, glue, etc should be intact. The implication for the internal contents is that they are as they left the factory. Any errors or imperfections (mint does not mean perfect!) were made by LEGO itself during the packaging process.

There is some controversy about whether collecting MISB is a worthwhile endeavour, or if the true destiny of every set is to be opened and to be played with or used.