Quantity supplied is a change in price along the supply curve. This is not to be confused by a change in supply, which would mean a shift of the supply curve.
A change in quantity supplied:
| \
P2|---\
| | \
P | | \
P1|---|-----\
| | | \
+--------------
Q2 Q1
Q
A change in supply:
| \ \
| \ \
|\ \ \
P | \ \ \
| \ \ \
| D3 D1 D2
+--------------
Q
Notice the difference? This happens to be a common mistake that has more to do with semantics than economics. It also illustrates how horribly anal economists are about definitions and their choice of words. Anyone who's taken an economics class can attest to that.