Heaviside unit function: Meaning and Definition of

Heav'iside u'nit func"tion

Pronunciation: [key]
— Math. Math.
  1. the function that is zero for any number less than zero and that is 1 for any number greater than or equal to zero.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.