Lumia Black is the latest update for Lumia Windows Phone 8 devices and combines goodies from GDR3 and Nokia’s Firmware. It typically has a version no. (3051.40000.134x.00xx).
To check for updates, on your phone, tap Settings -> phone update. Below is the official Changelog,
Daily delighters: lock the screen rotation, close apps easily in the app switcher, use custom ringtones for messaging and mail, among other things
Update to Nokia Camera that combines Nokia Smart Camera and Nokia Pro Camera. Available from the Store app.
Get the latest version of Nokia Glance Screen – see quick status notifications, for example, about calendar and messaging events on the lock screen. New night-mode colours for the Glance Screen
Bluetooth 4.0 LE – preserve energy while staying connected via Bluetooth
Get enriched camera performance, enhanced battery monitoring, and other stability and usability improvements
Nokia Camera, Nokia Storyteller for all. For 1 GB RAM devices- Nokia Refocus, Nokia Beamer.