i think Christian already gave a nice summary. I'd like to add that
LTP/LTD has basically nothing to do with short-term-plasticity (STP).
The first describing the change of synaptiv weights/efficiancy as
result corelated activity in both presynaptic and postsynaptic neuron.
The latter rather summarizes (mainly) presynaptic effects like vesicle
pool depletion, change of poolsize etc.
Whereas LTP/LTD are commonly associated with learning, STP seems to be
important for shaping activity patterns within spike trains.