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

brain dump
 n.

    [common] The act of telling someone everything one knows about a particular
    topic or project. Typically used when someone is going to let a new party
    maintain a piece of code. Conceptually analogous to an operating system 
    core dump in that it saves a lot of useful state before an exit. ?You'll
    have to give me a brain dump on FOOBAR before you start your new job at
    HackerCorp.? See core dump (sense 4). At Sun, this is also known as TOI
    (transfer of information).


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

brain dump

   (The act of telling someone) everything one knows about a
   particular topic.  Typically used when someone is going to let
   a new party maintain a piece of code.  Conceptually analogous
   to an operating system core dump in that it saves a lot of
   useful state before an exit.  "You'll have to give me a
   brain dump on FOOBAR before you start your new job at
   HackerCorp."  At Sun, this is also known as "TOI" (transfer of
   information).

   [Jargon File]