... for conversations about the sometimes confusing vocabulary of economics and how to teach it.
From chapter3, section 3.
Speaking economics: The balance of forces in equilibrium
Economists in the nineteenth century borrowed the word equilibrium from chemists and physicists. It comes from the Latin phrase aequa libra, which means "balanced scales." When the forces pushing price up and the forces pushing price down are equal, the scales are balanced and the market is in equilibrium.
An apple at the bottom of a bowl, for example, is "in equilibrium."