The North Sea, formerly also known as the German Ocean, is a coastal sea located in northern Europe covering around 220,000 square miles. In respect to Shetland, the North Sea lies to the east, south, and south east. While the southern limits of the North Sea are fairly well defined – Straits of Dover leading to the English Channel and the Skaggerak leading to the Baltic, the northern parts are open to the Norwegian Sea, and the North Atlantic. Mavis Grind is supposedly the only place where you can throw a stone from the North Sea to the Atlantic, but such claims are based on artificial divisions of seas (the North Sea is itself part of the Atlantic anyway, and such a claim could be made perhaps for certain other places in Shetland, or along the Pentland Firth and in Orkney as well)
The western parts of the North Sea are bounded by the British Isles, the east by continental Europe and Scandinavia. The northern coasts tend to be rockier, riven by fjords/firths, and often contain a number of islands e.g. Norway, Shetland, Scotland. The southern coasts tend to be low lying and muddy e.g. East Anglia, Friesland and around Bremen.
A major part of the north east is the Norwegian Trench, a deep channel following the coast of Norway. The deepest parts of the North Sea are nearer Shetland. Otherwise it tends to be a fairly shallow sea.
While the term, "German Ocean" disappeared with World War I, it is certainly true to say that it is perhaps a "Germanic Sea", i.e. nearly all the people along its shores speak Germanic languages, such as English, Flemish/Dutch, Frisian, German, Danish, Swedish, Norwegian etc. The two exceptions to this are Scotland perhaps, which had Gaelic speaking communities in the east Highlands and elsewhere, and parts of France and Belgium, where French has won out against Flemish.
The North Sea (with the exception of Norwegian waters) also falls entirely under the European Union, which means that the sea is under the European Common Fisheries policy.
It is still a massive global trade route, but most of the traffic tends to go via the English Channel. Some vessels do go round the north way, by Shetland, to get into the Atlantic but this is less common. The North Sea also gets a great deal of the Baltic and African/American Trade as well.
During the Ice Age it appears that humans were able to cross much of the North Sea on foot, and some of it seems to have been a large tundra, with mammoth and bison roaming. Animal and human artefacts have occasionally been trawled up from the sea bottom. The northern part of the North Sea appears to have been underwater, or at least under an ice pack. Areas such as Viking Bergen Island and Dogger Bank/Doggerland, seem to have remained above water for longer, ending up as marine banks.
The North Sea presented the Romans with the northern limits of their Empire. Later it became a migration route for the Saxons and the Norse. In the Middle Ages, a great deal of trading took place over it, notably by the Hanseatic League, the French, English and Dutch. With the discovery of the Americas, European attention turned westwards, and British ports such as Bristol, Liverpool and Glasgow gained a new importance, and overtook the old east coast ports in importance. The North Sea was also a major theatre in the two world wars.
In more recent times, the North Sea has become important for fishing, and for North Sea Oil and Gas. Gas fields tend to be in the south of the sea, and oil fields in the north of it.
The North Sea is affected by the North Atlantic Current, and the less saline outflow of the Baltic Sea, which create an anticlockwise circulatory pattern. Salinity tends to be highest around Shetland, and lowest near the Skaggerak and Kattegatt.
Major rivers entering the sea include the Rhine and the Elbe.
Because the North Sea countries were amongst the first in the world to become heavily industrialised, the sea has also struggled with serious pollution issues.