This refers to the time it takes for the motor to adjust its speed to different parts of the disk. One of the main advantages to the new CAV drives is that due to their constant speed they eliminate the speed change time entirely. Another factor is the seek time. This refers to the time it takes for the head to shift positions to where the requested data is located. This would vary depending on how far away it was at the time.
Latency refers to the amount of time the drive has to wait for the data to pass over the head.
CLV drives move faster on the outside of the disk and therefore, in those instances latency would be reduced. Perhaps the most popular measurement for CD-ROM performance is access time. Access time is the speed change time, the seek time, and latency combined. However, you can't simply add them up, because some of these operation go on simultaneously. Generally faster drives have faster access times.