WordNet (r) 3.0 (2006):

rotational latency
    n 1: (computer science) the time it takes for a specific block
         of data on a data track to rotate around to the read/write
         head [syn: rotational latency, latency]

The Free On-line Dictionary of Computing (30 December 2018):

rotational latency

    The time for the start of the required
   sector on a disk to appear underneath the read/write
   head.  The worst case is where it has just passed the head
   when the request is received.  For a disk drive with N heads
   per surface, rotating at R revolutions per minute, the average
   rotational latency will be

   	L = 30/NR seconds.

   Rotational latency is one component of access time.

   (2009-11-06)