pSD

PSD is an acronym that can refer to several distinct concepts across different domains. In computing and graphics, PSD most commonly denotes Photoshop Document, the native file format used by Adobe Photoshop. PSD files preserve image data with multiple layers, masks, channels and alpha information, enabling non-destructive edits. They support high color depth and can be saved with various compression options; many other programs can import or export PSD files, although some features may be lossy or unavailable outside Photoshop.

In signal processing and statistics, PSD stands for power spectral density, a function that describes how the power of a signal is distributed across frequency. The PSD is derived from the Fourier transform of the signal's autocorrelation and is used to analyze noise, vibrations, and other time-series phenomena. It is typically expressed in units of watts per hertz (or variance per frequency) and can be estimated through methods like periodograms or Welch's method.

In politics, PSD refers to several political parties, particularly in Portuguese-speaking countries. The most prominent is the Partido Social Democrata in Portugal, a center-right party founded in the 1970s. Other countries, including Brazil, have or have had parties called Partido Social Democrata as well; the exact platform and history vary by country.

Other uses exist in technical and organizational contexts, but the three examples above cover the most common meanings. When encountering the acronym PSD, it is usually necessary to rely on surrounding context to determine the intended sense.