A simple definition of scientific management might be "a theory which suggests there is a 'best way' to perform work tasks".
A more formal definition is: "Management of a business, industry, or economy, according to principles of efficiency derived from experiments in methods of work and production, especially from time-and-motion studies."
Although anticipated by Babbage, the theory was formalised by Taylor, and first published in his book Shop Management (1903). It was developed in various ways by Gant, Frank Gilbreth and Hopf.
Although scientific management as a distinct theory or school of thought was obsolete by the 1930s, most of its themes are still important parts of industrial engineering and management today.