The "EV" designation refers to the "evolution" of the Mindstorms product line.
"3" refers to the fact that it is the third generation of computer modules - first was the RCX and the second is the NXT.
The main processor of the NXT was an ARM7 microcontroller, whereas the EV3 has a more powerful ARM9 CPU running Linux.
LEGO has also released instructions online to build 12 additional projects: ROBODOZ3R, BANNER PRINT3R, EV3MEG, BOBB3E, MR-B3AM, RAC3 TRUCK, KRAZ3, EV3D4, EL3CTRIC GUITAR, DINOR3X, WACK3M, and EV3GAME.
It uses a program called LEGO Mindstorms EV3 Home Edition, which is developed by LabVIEW, to write code using blocks instead of lines.
Robots that can be built with the expansion set are the Tank Bot, the Znap, the Stair Climber, the Elephant and a remote control.
EV3 software can be used to program the NXT, but some extra programming-blocks must be downloaded, such as the Ultrasonic sensor (which is included in the standard NXT kit, but not the standard EV3 kit).
This enhancement allows for smoother rotation at low speed and better position control.