X (pronounced ten) is the eighth studio album by British rock band Def Leppard, released in 2002. Much like 1996's Slang, it featured another departure from their signature sound by moving into the pop genre. The album charted at #11 on The Billboard 200 and #14 on the UK Albums Chart. Most of the album was produced by Pete Woodroffe and the band, with remaining tracks produced by either Marti Frederiksen or Per Aldeheim and Andreas Carlsson. This is the first Def Leppard album in which drummer Rick Allen actively took part in song-writing. On all of the band's prior albums, he is only credited with helping co-write 3 tracks. On this album alone, he co-wrote 11.
The album features the Roman numeral 'X', recognising it as their tenth album release, although the album is in fact only their eighth collection of all-new studio material. The other two albums released by the band prior to the release of X, Retro Active and Vault, were a rerecording of B-sides and rarities and a greatest hits set respectively.
The album did not sell to the standards of their previous releases and failed to earn any RIAA-certification. Nothing from this album has been performed live by the band since the conclusion of its supporting tour.