The inequality (1) derives the name ``uncertainty principle'' from its interpretation in quantum mechanics. Observations of subatomic particles show they behave like waves with spatial frequency proportional to particle momentum. The classical laws of mechanics enable prediction of the future of a mechanical system by extrapolation from the currently known position and momentum. But because of the wave nature of matter, with momentum proportional to spatial frequency, such prediction requires simultaneous knowledge of both the location and the spatial frequency of the wave. This is impossible, as we see from (1); hence the word ``uncertainty.''