Most generally, this means to "decrease the effect of", or "decrease the effectiveness of".
In biological neural terms, depression is the reduction in the ability of a signal (an action potential
) at a synapse
to affect the post-synaptic neuron
. Depression is the reduction in the strength of a synaptic connection between the pre- and post-synaptic neurons connected through a synapse. Depression is the opposite of potentiation
Depression is not inhibition
. An inhibitory synapse
can undergo post-tetanic, and long-term-depression
, and LTD
respectively). In other words, depression of an inhibitory synapse
means to make it less likely to inhibit the firing of its neuron.