The Collaborative International Dictionary of English v.0.48:

baseline \baseline\ n.
   1. an imaginary line or standard by which things are measured
      or compared; as, they established a baseline for the
      budget.
      [WordNet 1.5]

   2. the back line at each end of a tennis court.
      [WordNet 1.5]

   3. (Baseball) the lines between bases on a baseball field
      along which a baseball player must run while running the
      bases.
      [WordNet 1.5]

   4. a measurement that represents the value of a physical
      quantity (such as a voltage, or a level of radioactivity)
      in the absence of effects from other variables in a
      measurement, test or experiment; a control value.
      [PJC]

   5. any horizontal line in a plot, graph, or diagram, or on a
      visual display in an electronic device, used as a
      reference point to which other values are referred.
      [PJC]

WordNet (r) 3.0 (2006):

baseline
    n 1: an imaginary line or standard by which things are measured
         or compared; "the established a baseline for the budget"
    2: the back line bounding each end of a tennis or handball
       court; when serving the server must not step over this line
       [syn: service line, baseline]
    3: the lines a baseball player must follow while running the
       bases

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

release
baseline
released version

    (Or "released version", "baseline") A version of
   a piece of software which has been made public (as opposed to
   a version that is in development, or otherwise unreleased).

   A release is either a major release, a revision, or a
   bugfix.

   Pre-release versions may be called alpha test, or beta
   test versions.

   See change management.

   (1996-08-04)