We derive viking, or vikings, from the Old Norse word vikingr. In Old Norse it referred to sea-voyagers particularly sea-borne pirates and raiders. The “vik” part comes the Old Norse word for a bay or inlet. “ingr” is a suffix that indicates being “from”, thus “vikingr” means “one from the bays”. Naturally sea voyagers and sea-borne raiders would be coastal rather than inland people.
Today we tend to use the word for all the nordic people of the Viking Age. So we may call a sword of a design common at the time of the Viking Age a “viking sword”, though vikings would not be the only ones to have them. Also not all the nordic peoples were vikingr.
It is the sea voyaging of the vikingr which define the age we call the Viking Age.
Necessity is the mother of invention. Thus the geography of Scandinavia may be a particular cause for precipitating the great developments in the craft of sea travel which is distinctive of the Vikings.
The land is harsh and rather poor for farming. This increases the relative importance of fishing for nutrition and so also make coastal dwelling especially desirable.
Moreover the coastline is exceedingly ragged, featuring deep inlets called fjords. These fjords considerably lengthens journeys by land for coastal dwellers by forcing indirect routes. This makes journeys by sea relatively more efficient.
The people with whom the vikings interacted either as raiders or traders probably would not have used the term viking to describe them. Anglo-saxon sources refer to the raiders as the Danes. While those that settled in the British Isles were referred to by the place names of their settlements such as York.