The Free On-line Dictionary of Computing (19 January 2023):

TCB

   1.  Trouble Came Back.

   2.  (Orange Book) Trusted Computing Base.

   3.  Task Control Block.

   [Jargon File]

   (1998-07-02)


The Jargon File (version 4.4.7, 29 Dec 2003):

TCB
 /T·C·B/, n.

    [IBM] 1. Trouble Came Back. An intermittent or difficult-to-reproduce
    problem that has failed to respond to neglect or shotgun debugging.
    Compare heisenbug. Not to be confused with:

    2. Trusted Computing Base, an ‘official’ jargon term from the Orange Book
    .