A graded depolarization or decrease in electrical potential across the membrane of a postsynaptic neuron, occurring in response to a signal transmitted across a synapse by a presynaptic neuron, increasing the propensity of the postsynaptic neuron to initiate a nerve impulse. Also called postsynaptic excitation. See also action potential, depolarization, postsynaptic potential, resting potential. Compare inhibitory postsynaptic potential. EPSP abbrev.