PSD can stand for: Politics · Social Democratic Party, a political party of Portugal. · Social Democratic Party, a political party of Romania. · Socialist Destourian Party, the old name (to 1988) of the ruling party in Tunisia, currently called Constitutional Democratic Rally. Travel · IATA code for Port Said Airport, Port Said, Egypt Sciences · Particle size distribution, in many branches of science and technology. · Phase sensitive detector, in electronics. · Position sensitive device or position sensitive detector, a device that measures the one or two-dimensional position of a lightspot. · Positive-semidefiniteness as it relates to matrices. · Postsynaptic density, a specialization of the cytoskeleton at the synaptic junction. · Post Source Decay, a technique used in MALDI mass spectrometry