power per unit time into frequency components composing that signal. Medicine Protein S deficiency Post-stroke depression Postsynaptic density, a specialization of the cytoskeleton at the synaptic junction Psychiatric service dog Other uses in science and engineering Particle size distribution, in granular materials Platform screen doors, on railway platforms Position sensitive device or detector, a two-dimensional photodetector Positive semidefinite (disambiguation) Power spectral density, distribution of power of a signal Program Service Data, data displayed on HD radio receiver Other uses PSD (rapper), a Californian rapper and hip-hop producer Port Said Airport, Egypt (IATA code PSD) Private Sector Development, term used in international development PSD Bank, German banking group