Complex sentence: A gratuity (also called a tip) is a sum of money customarily tendered, in addition to the basic price, to certain service sector workers for a service performed or anticipated.
Split into simpler sentences: A gratuity (also called a tip) is a sum of money customarily given by a client or customer to a service worker, in addition to the basic price. Tipping is commonly given to certain service sector workers for a service performed or anticipated.