Linked from
The 9 pages that link to Electric flux, each with the reason it gives.
Electric fieldRelated: Flux summarizes the field crossing surfaces used in Gauss's law.
ElectrostaticsRelated: Flux connects electric fields to enclosed charge in Gauss’s law.
Ampère's circuital lawRelated: Its time variation supplies the displacement-current contribution.
Gauss's lawRelated: It is the quantity Gauss's law integrates across a closed surface.