Bisque refers to any pottery that has been fired in a kiln without a ceramic glaze.  Bisque firing is the process to transform unfired bone-dry clay from its fragile state to a porous and durable state.  This stage of the process is essential because now you can safely glaze to the piece without damaging or cracking it.  My bisque firing is to cone 06, approximately 1,828 F.  The second stage of my process is the glaze firing at cone 6, approximately 2,232 F.