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

break-even point
 n.

    In the process of implementing a new computer language, the point at which
    the language is sufficiently effective that one can implement the language
    in itself. That is, for a new language called, hypothetically, FOOGOL, one
    has reached break-even when one can write a demonstration compiler for
    FOOGOL in FOOGOL, discard the original implementation language, and
    thereafter use working versions of FOOGOL to develop newer ones. This is an
    important milestone; see MFTL.

    Since this entry was first written, several correspondents have reported
    that there actually was a compiler for a tiny Algol-like language called
    Foogol floating around on various VAXen in the early and mid-1980s. A
    FOOGOL implementation is available at the Retrocomputing Museum http://
    www.catb.org/retro/.


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

break-even point

   In the process of implementing a new computer language, the
   point at which the language is sufficiently effective that one
   can implement the language in itself.  That is, for a new
   language called, hypothetically, FOOGOL, one has reached
   break-even when one can write a demonstration compiler for
   FOOGOL in FOOGOL, discard the original implementation
   language, and thereafter use working versions of FOOGOL to
   develop newer ones.  This is an important milestone.  See My
   Favourite Toy Language.

   [There actually is a language called Foogol].