sheaf
collection of objects associated to subsets of a space in a manner admitting gluing and restriction
torsion sheaf
sheaf on a site for which, for every quasi-compact U, the space of sections is a torsion group
flabby sheaf
sheaf in which restriction maps are always surjective, so that sections can always extend
locally constant sheaf
Sheaf theory
algebraic space
generalization of a scheme; an étale equivalence relation on a scheme; a sheaf of sets on the big étale site with representable diagonal morphism and a surjective étale morphism from a scheme