| Jack of all trades, master of none | A person, business, or other entity who has become a generalist. Due to a lack of specialization, a jack of all trades will usually find himself unable to match the efficiency, quality, and ability offered by a master. |
| Japanese auction | A bidding system in which price continually rises until only one bidder is willing to pay. He then pays the highest price that attracted at least one other bidder. |
| Jevons paradox | The result of research on coal usage by William Stanley Jevons. It states that increasing efficiency of the use of an item will cause more of that item to be used. |
| Joint surplus | The sum of the economic rents of all involved in an interaction. Also known as: total gains from exchange or trade. |
| Joule | A unit of energy or work, originally defined as the amount of energy necessary to lift a small apple vertically 1 metre. |
| Juda Principle | People prefer to maximize the appearance of acquired skills and expended effort over the creation of actual value. |
| Junk silver | A silver item that has no value over and above the value of the metal itself. |
| Justification letter | A document intended to convince the recipient to act in a specific manner. The letter will generally focus on the benefits of a desired course of action. |
