A building to function properly and fulfill the needs of its occupants, it has to be dressed by different types of Mechanical, Electrical and Electronic services. In general, these services are called Building Services.
A building can be dressed with HVAC system, Plumbing System_ Taps, Kitchen Basins etc. It can have Drainage System or Fire Fighting System. For Hospitals, we can have Medical Gas Services such as Oxygen, Nitrogen, Medical Air, Vacuum systems.These are Mechanical systems needed in order for a building to function properly.
Similarly, We have Electrical and Electronic system for a Building. Electrical system covers High Voltage Electrical systems such as Power, Transformer, if needed, distribution boards and wires to connect to Lighting system, OR provide Power to a switch.