What is repetition and why is it used?

The act of repeating; a doing or saying again; iteration., Recital from memory; rehearsal., The act of repeating, singing, or playing, the same piece or part a second time; reiteration of a note., Reiteration, or repeating the same Word, or the same sense in different Words, for the purpose of making a deeper impression on the audience., The measurement of an angle by successive observations with a repeating instrument.