A soul net is an Integrator-made device intended to restrict the mobility of reapers.
A soul net produces a soul-empowered magnetic field which prevents reapers from passing through. The range of a single piece of soul net is fairly short, so a network is required to restrict access to a moderately sized or larger area.
If a group expects to maintain dominance in an area, soul nets can be put in the ground as a way to keep enemy reapers from sneaking in from beneath and raising their servants within to cause mischief. It will also make it more difficult for a reaper to escape underground if their servant is defeated, although this may backfire since the side that created a soul net will not be able to deactivate it quickly unless they built in a mechanical deactivation system for the electricity.
In theory a soul net could also be used to imprison reapers, but in practice a soul-empowered physical container is usually a simpler and more reliable alternative.
In order to create a soul net, an Integrator needs access to a network of power lines. They will fuse the power of their soul with the wire, and when the power is turned on the magnetic field that electrical current naturally projects will be impregnated with the creator's (or that of someone more powerful who helped) soul. As far as the magnetic field reaches with a certain level of power, reapers will not be able to enter.