Complimentary services or products are those given to an audience / a customer without charge. This term is often used in the tourism and hospitality industry.
Examples: Complimentary bottle of water in your room, free Wifi, complimentary room service, an upgrade to a higher room category without additional costs.
Another example can be: A client or a group staying in your hotel books a conference room. Within the conference room there are other services included, like: Wifi, projector, water, coffee and cookies, notebooks and pens. Those ‘extras’ are complimentary services (they are calculated into the conference room package price but for the customer they are ‘complimentary’)