Short for constant angular velocity, a technique for accessing data off of rotating disks. With CAV, the disk rotates at a constant speed regardless of what area of the disk is being accessed. This differs from Constant Linear Velocity (CLV), which rotates the disk faster for inner tracks. Disk drives use CAV, whereas CD-ROMs generally use CLV, though some newer drives use a combination of CAV and CLV.
The advantage of CAV is that it is much simpler to design and produce because the motor doesn't need to change speed. In addition, CLV runs into problems for very high-speed CD-ROMs because there's a brief latency whenever the drive needs to change the rotational speed.