Respuesta: períodos de prohibición de venta (de valores)

Explicación:
Blackout Periods
Obviously, from the title you can figure out that blackout periods means that something gets stopped. In this case securities law has times where you can't sell your stock and they call them "blackout periods." These periods can affect the federal taxes that would usually hit you at the time you exercise. Normally the money you receive from your option exercise would be considered the same as your regular income and of course, you can count on it being taxed that way too. That regular income amount is determined from the difference between the exercise price and the fair market value at the time of exercise. However, because of those blackout periods that form of taxes doesn't always work, like when securities law prohibits you from selling the stock at the time of option exercise.



Referencias:
//http://www.myoptionvalue.com/movschool/NSO_Blackout.html