ℓ-adic sheaf

In algebraic geometry, an ℓ-adic sheaf on a Noetherian scheme X is an inverse system consisting of ${\displaystyle \mathbb {Z} /\ell ^{n}}$-modules ${\displaystyle F_{n}}$ in the étale topology and ${\displaystyle F_{n+1}\to F_{n}}$ inducing ${\displaystyle F_{n+1}\otimes _{\mathbb {Z} /\ell ^{n+1}}\mathbb {Z} /\ell ^{n}{\overset {\simeq }{\to }}F_{n}}$.

Bhatt–Scholze's pro-étale topology gives an alternative approach.