The fpqc topology is a Grothendieck topology on the category of (commutative) affine schemes. It is one of the main Grothendieck topologies used in algebraic geometry.
Let be the category opposite to the category of commutative algebras. A family of maps in that category is a cover in the fpqc topology if the union of images cover as a topological space and all morphisms are faithfully? flat and quasicompact. The French for this is fidèlement plat et quasicompact (fpqc).