Actually, NCL does
call it a service charge:
Traditionally, gratuities for all the service you experienced aboard an NCL ship were paid at the end of the cruise. This often led to a last-night scramble as guests tried to find the correct amount of cash to place in each tip envelope. For your convenience, NCL now automatically applies a service charge to your shipboard account: $10 per guest per day for guests age 13 and above, $5 per day for children age 3-12 and no charge for children under the age of three. All of the service personnel on board receive gratuities from this service charge, and there is no need for you to think about additional tipping. Separately, a 15% gratuity is added for bar drinks and spa services.
So what NCL charges you is a "service charge." They give gratuities to the staff from the money they raise by charging you the service charge. 100% accurate language.