Isocrystal
In algebraic geometry, isocrystals are p-adic analogues of Ql-adic étale sheaves, introduced by BerthelotandOgus (1983) (though the definition of isocrystal only appears in part II of this paper by Ogus (1984)). The term isocrystal stands for roughly "crystal up to isogeny". Convergent isocrystals are a variation of isocrystals that work better over non-perfect fields, and overconvergent isocrystals are another variation related to overconvergent cohomology theories.