Why pitch is not the same as frequency

from blog Kevin Boone's website, | ↗ original
In many cases, "pitch" is just the musician's way of saying "frequency". However, pitch has a perceptual element to it, and the ear can be fooled. This article explains one of the ways in which this can happen, and why it isn't correct to use the terms "pitch" and "frequency" interchangeably in music.