In Pavlov, inhibition describes any reduction in positive response to a stimulus. This is not necessarily analogous to the use of the term to describe synaptic responses in biological and artificial neural networks. For more details on Pavlov's usage, see Extinction
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In biological neurons, inhibition describes a property of a synapse or synaptic response that causes the neuron to be less likely to fire when it is stimulated. For more about this, see the entry here entitled Inhibitory Synapse.
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In artificial neural networks, an inhibitory synapse is a synapse, which is historically represented with a negative weight value. The inhibitory synapse modulates the stimulation by the negative weight, causing the neuron's output to become less positive.
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In any case, inhibition is not the same as depression, which is the decrease of the input's ability to have any effect on its neuron's output, positive or negative.