Instant Meshes Remesh, as you might guess is an addon to remesh your mesh. For example when you sculpt with Dynotopo, the topology is so ugly that you need to remesh it. This can be done by hand but it takes usually a lot of time. Sometimes you can get away with automatic remesh. Blender has a build in Mesh modifier, but Instant Meshes Remesh that uses the Instant Remesh software is more sophisticated.
