It is the energy possessed by a body because of the interactive forces inside the object. This may be defined as the work done in assembling all the particles of a body in a exact shape and size or it is the work done in creating a body. We can say that if the forces inside the body are attractive, work done in assembling is done by the body itself and self energy of the body will be negative and if the forces inside the body are repulsive then some external work will be completed in assembling the body and its self energy will be positive. As gravitational self energy of an object is concerned obviously it is always negative because of attractive forces.