Linked from
The 39 pages that link to Poisson's equation, each with the reason it gives.
Electric potentialRelated: It determines electric potential from charge density in a region.
Newtonian gravityRelated: It relates the gravitational potential to the distribution of matter.
LaplacianRelated: It uses the Laplacian to connect fields to their sources.
EquipotentialRelated: It determines potential curvature where charge or mass sources are present.
Gauss's law for gravityRelated: It is the differential form of the gravitational flux law.