The EPS discharge was a discharge of the electro-plasma system.

In 2370, when the USS Enterprise-D found itself trapped in a subspace rift caused by the activation of the USS Fleming warp drive, William T. Riker asked Data if they could do an EPS discharge through the impulse reactor. Data did not think it would work, adding that the resulting explosion might destroy the saucer section. (TNG: "Force of Nature")