NUA isn't the latest channel available on your cable TV system. It stands for "net unrealized appreciation"—a little-known gem of a tax break for those who take payouts in the form of company stock from a 401(k) or other employer-sponsored retirement plan.

This tax law provision lets you benefit twice: once when you pay the tax on the plan distribution and once when you sell the stock.

If you receive a retirement plan distribution in company stock, you'll be taxed only on what you initially paid for it. You won't have to pay tax on any subsequent gains in value—known as net unrealized appreciation, or NUA. In contrast, cash distributions from your 401(k) normally are taxed as income, at rates up to 39.6%.