| Zero degree homogeneous | Homogeneous of degree zero. |
| Zero profit | A situation in which profit in an industry is zero, usually as a result of free entry and exit. It may, if firms are not identical, refer only to the marginal firm. And it always means zero excess profit, not that all returns to capital invested in the industry are zero. |
| Zero substitution | An elasticity of substitution of zero. In a production function, this means a Leontief technology. |
| Zero sum game | A game in which the payoffs to the players add up to zero, so that a gain for one is necessarily equaled by loss to others. Contrasts with positive sum game. |
| Zeroing | The practice used by the U.S. in calculating dumping margins of treating individual prices that are above the fair price as being instead equal to that fair price, so that the average price is necessarily at or below the fair price and the dumping margin is positive. |
| Zipf's Law | The regularity noticed by Zipf (1949) that, within any country, the populations of cities are close to proportional to 1/r, where r is the population rank of the city. Thus the largest city has about twice the population of the second largest, three times the population of the third largest, etc. |