Bisque is that state when
pottery is fired in a low temperature
kiln (cone 4 or so) to create a piece which is porous and semi-brittle. It absorbs
glaze efficiently and uniformly. The piece of pottery is then fired in a much higher temperature kiln (cone 8-12).
Bisqueware is not limited to porcelain.
Greenware, or unfired pottery can be glazed, but the results are more serendipitous.