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

Task Control Block

    An MVS control block used to communicate
   information about tasks within an address space that are
   connected to an MVS subsystem such as MQSeries for
   MVS/ESA or CICS.

   FAQ

(http://www-4.ibm.com/software/ts/mqseries/library/manuals/csqfao/CSQFAO22.HTM).

   (2000-12-30)