What he is saying is that the spark advance is controlled by the advance curve in the distributor, advance means 'to move forward'. The advance mechanism rotates the trigger mechanism of the distributor, advancing it in relation to the distributor shaft. The amount of advance is controlled by a pin in a slot that limits the travel of the mechanism. The rate of advance is controlled by weights and springs. If you have a 25° advance curve, it will advance the timing 25° within its rpm range of operation. If you set it to start at 15°, it will advance to 40°. If you set it to start at 5° it will advance to 30°.
Spark timing is the point at which the spark is triggered, and this is controlled by rotating the distributor body in relation to the shaft. Rotating the distributor will always change the timing, and it will set the boundaries of the advance curve.
"For those that will fight for it...FREEDOM ...has a flavor the protected shall never know."
Semper Fi! L/Cpl Edwin L. "Tim" Craft, B Co 3rd AT's, Khe Sanh Combat Base, February, 1968