To lose value.

For example, when you drive that new Bugatti off the lot at your dealership, that car starts depreciating about as fast as you drive. Because it's no longer new, it’s automatically worth less than it was an hour ago—even if it still has the new car smell. Cars aren't the only things affected, by the way. Business equipment, computers, and other stuff can depreciate, too, and businesses need to keep track of depreciation to understand what their stuff is worth. If you owe $100,000 in loans for factory equipment, for example, and that equipment is now worth only $50,000 thanks to the amazing powers of depreciation, that’s something you're going to want to keep an eye on.

For people keeping the books at a company, it's the process of assigning the decline in value of a license or product over time. Say you buy a computer for $3,600. The law says that you must depreciate it $100 a month for 36 months until, on your books, it's valued at zero. The thinking is that, at the end of the period, you "know" you have to buy another computer. Many computers last more than 3 years, though, so the numbers get all messed up.

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