According to Google...

• NUA represents the increase in value of your employer's stock from its initial purchase price (cost basis) to its market value on the date of distribution from your retirement plan.
• When you take a lump-sum distribution of company stock from your qualified retirement plan and transfer it to a taxable brokerage account, you only pay ordinary income tax on the cost basis of the stock in the year of distribution.
• The NUA portion is deferred and taxed at the lower long-term capital gains rates when you eventually sell the stock in the brokerage account.
• Any additional gain after the distribution to the brokerage account is taxed as short-term or long-term capital gains, depending on how long you hold the stock.