one's age, according to the traditional Chinese method of reckoning (i.e. the number of Chinese calendar years in which one has lived). In this system, a person's age is one year at birth, and increases by one year at the beginning of the first solar term 立春[Li4 chun1] each year, rather than on one's birthday.
as opposed to 足歲|足岁[zu2 sui4]
see also 實歲|实岁[shi2 sui4]