Also often shown as quality, time and resources. Commonly rendered in a diagram using a triangle, with each side labelled with one choice, and a big $ in the middle. The idea being that the PHB or marketroid
you're showing it to will then intuitively grok the idea that they can't increase one without decreasing another, or spending more $ or both.
In practice drawing the diagram makes the PHB or marketroid daydream about the kind of interlocking brick they want on the jacuzzi patio. But at least you tried.