In the execution of a computer program, (a) the elapsed time between (i) the instant execution begins and (ii) the instant execution is completed or (b) any instant during the execution of the program. Note: The execution time may be processor time, wall-clock time, or time on the Coordinated Universal Time scale. See  program execution time. Synonyms  running time,  run time. See also  computer program,  Coordinated Universal Time,  processor time,  time of occurrence,  wall-clock time.