PDE may refer to: PDE, as initial letters of words: Partial differential equation, differential equation involving partial derivatives (of a function of multiple variables) The European Democratic Party (esp. in Spanish, French or Italian languages) Present Day English Principle of double effect Program development environment Pug dog encephalitis Pulse detonation engine, proposed substitute to the traditional jet engine Punta del Este Other modes of abbreviation: Phosphodiesterase, enzyme important in intracellular communication Polydichloric euthimal, fictional substance Pde (or Pde.), "Parade" (when serving as part of the proper name of a street or other way)