Étale topology
GROTHENDIECK TOPOLOGY ON THE CATEGORY OF SCHEMES, WHOSE COVERING FAMILIES ARE JOINTLY SURJECTIVE FAMILIES OF ÉTALE MORPHISMS
Etale topology; Étale sheaf
In algebraic geometry, the étale topology is a Grothendieck topology on the category of schemes which has properties similar to the Euclidean topology, but unlike the Euclidean topology, it is also defined in positive characteristic. The étale topology was originally introduced by Grothendieck to define étale cohomology, and this is still the étale topology's most well-known use.