Complex sentence: 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.
Split into simpler sentences: In algebraic geometry, the étale topology is a Grothendieck topology on the category of schemes which has properties similar to the Euclidean topology. In characteristic zero, it is equivalent to the Euclidean topology, but unlike the Euclidean topology, it is also defined in positive characteristic.