The correct answer is "airbridge". Jetway is a trade name of the FMC Jetway Corporation who are a major manufacturer of airbridges.

A pier is a building structure, like a pier into the sea, usually an integral part of the terminal building althoufgh there are a few freestanding ones around. Piers can have aircraft on one or both sides. Most commonly there are a number of airbridges at gates along the pier.

Although most gates have one airbridge there are a few which are used for widebody aircraft which have two airbridges, allowing two streams of passengers to enter an aircraft at once through separate aircraft doors.

The pier constructed at Gatwick when the new airport opened in 1958 was a simple structure out across the ramp with aircraft on both sides. You still had to go out and walk across the ramp to aircraft steps.

It is ambiguous to say Gatwick has been around for 70 years. It was opened in 1936 but fell into disuse within a couple of years because, although it had a novel terminal building and its own rail station, the runways were still grass and they suffered from extensive flooding in winter, and all airlines withdrew services. In 1958 a new airport opened using part of the same site, but it had a new railway station in a different place and a new, resited terminal. The 1930s circular terminal building, generally known as "The Beehive", has been offices for many years now.