Your question really needs more information. Generally speaking, "deferred" means something is put off until another time, like deferred payments. So, whatever is being deferred in your case is being put off until you, or the person you're asking about, is age 59.
As another said, it means "put off" until you are 59. At one time, one could not withdraw any retirement money from a 401K plan until they were 59 1/2 years old. The money was "deferred" payment until that time.