Hi Wazzle,
it is a match to 5 points
white's score is 2, black's score is 1.
Black has doubled so we play for 2 points now.
If white gets the upper hand later in the game, he can redouble the cube to 4.
If white then wins the game he will score 4 points and win the match at a score of 6-1,
but he would already have won if he had only scored 3 points, since the match is to 5 points.
This 1 point difference 6 versus 5 is a wastage of 1 point.
If black would have won the score would be 2-5, so black would win the match exactly, without wastage.
Overage is the same as wastage.
White will not so soon redouble to 4 (= his recubes are hampered), because black needs exactly 4 points to win the match.
So if the game goes the wrong way, white will not get another chance to try and win the match.
To explain "taking deeper than money" i use another example. Say that you play a long 15-point match and the score is 13-1 for white.
White offers a double, for money the gammonless take point for black is when he has 25% chance.
But in a 15-point match black's chances after passing the cube (the score is then 14-1) are only about 2%.
In that case black's take point is 2%, he can take 23% deeper than for money.
Any chance higher than the 2% after passing is good for black, so he would be happy to take if he had for instance only 5% of winning.
The 5-point match is very special, read the next article and you understand why:
http://www.bkgm.com/articles/GOL/Aug99/fivept.htm