OK, that was glib. Here's a real definition: A Stableford competition employs a points system that is set forth in the Rules of Golf under Rule 32. A Modified Stableford is a competition that employs the same principle - golfers are awarded points based on their performance on each hole, with the highest point total winning - but with a different set of points than what is described in the rulebook.
Modified Stableford is better known than Stableford because a PGA Tour event, The International, is played using Modified Stableford. At The International, points are awarded on this scale:
Double Eagle: 8 points
Eagle: 5 points
Birdie: 2 points
Par: 0 points
Bogey: -1 point
Double Bogey or Worse: -3 points
(To see how this compares with the rulebook Stableford scoring, check out the Stableford definition.)
A Modified Stableford can have different point totals for different accomplishments as a tournament committee decides. It can also offer different points to different players for the same accomplishments.
For example, if handicaps are not being used in competition, they can be used to flight players into A, B, C and D. Then points are adjusted so that, as an example, a par gets an A player 0 points, a B player 1 point, a C player 2 points and a D player 3 points.
For further explanation, please see: How to Play Stableford or Modified Stableford Competitions

