Services are defined as subsidiary activities of the economy. This sector is characterized with a variety of heterogeneous activities: real estate activities, renting of machinery and goods, computer and related activities, accountancy and tax advice services, legal services, architectural and engineering services, technical testing and analysis, advertising, market research, labour recruitment services and other personal services.

The main characteristics of the services sector are: the intangible output; the interaction between the producer and the client, and its knowledge-intensive services.

Services are supplied to firms or administrations - for the support of their production processes or organization - rather than to households.