Definition for Excitatory postsynaptic potential (EPSP)
From Biology Forums Dictionary
1) The response from an excitatory neurotransmitter depolarizing the postsynaptic membrane; the depolarization brings the membrane potential closer to the threshold potential that would trigger an action potential.
2) An excitatory postsynaptic potential is a temporary depolarization of postsynaptic membrane potential caused by the flow of positively charged ions into the postsynaptic cell as a result of opening ligand-sensitive channels - a postsynaptic cell is defined as excitatory if it makes it easier for the neuron to fire an action potential, EPSPs can also result from a decrease in outgoing positive charges - the EPSP excites the next neuron and is dependent upon excitatory transmitters.