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Personal digital assistant, an electronic device which can include some of the functionality of a computer, a cellphone, a music player and a camera

Pathological Demand Avoidance, a condition within the Autistic Spectrum

Pitch detection algorithm, a mathematical method of finding the pitch of a signal

Public display of affection, an area of study within social psychology

Patent ductus arteriosus, a congenital heart defect

Pushdown automaton, a type of abstract device in automata theory

Progressive Democratic Alliance, an historical political party in British Columbia, Canada

Progressive Democrats of America, a political organization in the United States

Pakistan Domestic Airlines (PDA), the internal National flag carrier which is part of the wider branch of PIA

Past Doctor Adventures, a series of spin-off novels based on Doctor Who

phase-Doppler analyzer, a kind of instrument for measure particle volecity and size

Polydiacetylenes

Polo Democratico Alternativo, (Alternative Democatic Pole), a political party in Colombia

Private defense agency

"PDA," a song by Interpol from their 2002 album Turn on the Bright Lights

Posterior descending artery, one of the coronary arteries

Panic Disorder with Agoraphobia, discussed at Panic attack#Agoraphobia

Perception-Decision-Action, a model of cognition

Pinoy Dream Academy, Philippine version of Star Academy

"PDA", the former band of Dani Filth

PDA is an episode title of Aqua Teen Hunger Force