Over 100 years ago, it arose the necessity of using existing terrains to carry out the first flights. Those terrains were named airfields. Later on, airfields evolved to what is referred to as aerodrome. ICAO, in its Annex 14 ICAO  defines aerodrome as:
A defined area on land or water (including any buildings, installations, and equipment) intended to be used either wholly or in part for the arrival, departure, and surface movement of aircraft.
After World War II, when commercial aviation reached its maturity, the term airport was generalized. The term airport refers to an aerodrome that is licensed by the responsible government organization (FAA in the United States; AESA in Spain). Airports have to be maintained to high safety patterns according to ICAO standards.
An airport is an intermodal transportation facility where passengers connect from/to ground transportation to/from air transportation. As it will be described in detail in Section 9.3, airports can be divided into land-side and air-side. The land-side embraces all facilities of the airport in which passengers arrive/depart the airport terminal building and move through the terminal building to clear security controls. Air-side embraces those infrastructures devised for movement of the airplanes on the airports surface, but also the boarding lounges. Roughly speaking, land-side corresponds to those facilities in which both passengers and companions (not passengers such as family, friends, etc.) cohabit. On the contrary, air-side infrastructure include all those areas in which only passengers with tickets (and obviously also airport employees) are allowed to be, including those infrastructures made for aircraft parking, taxiing, and landing/taking-off.
The most simple airport consists of one runway (or helipad), but other common components are hangars and terminal buildings. Apart from these, an airport may have a variety of facilities and infrastructures, including airline’s services, e.g., hangars; air traffic control infrastructures and services, e.g, the control tower; passenger facilities, e.g., restaurants and lounges; and emergency services, e.g., fire extinction unit. A more general definition could be as follows:
A localized infrastructure where flights depart and land, acting also as a multi-modal node where the interaction between flight transportation and other transportation modes (rail and road) takes place. It consists of a number of conjoined buildings, flight field installations, and equipments that enable: the safe landing, take- off, and ground movements of aircraft, together with the provision of hangars for parking, service, and maintenance; the multi-modal (ground-air) transition of passengers, baggage, and cargo. From a socioeconomic perspective, airports can be also considered a pole for economic growth, a door-gate of a country-region, and an entertainment area (shopping, eating & drinking).