A type of postsynaptic potential where the binding of neurotransmitters with the postsynaptic receptors causes the opening of ion channels which results in depolarization (or the net gain of positive charge across the membrane) and thus the firing of action potential from the postsynaptic cell.
In general, the resting potential of a neuron is about -70mV and the firing threshold of an action potential is about -50mV. When there is a net gain of positive charge across the membrane of a postsynaptic neuron, the potential comes closer to zero or to the firing threshold. In such a case, the postsynaptic potential is excitatory since the probability to fire an action potential is likely.
Compare: inhibitory postsynaptic potential