There is no exact geographical definition of what precisely belongs to the region of Northern Europe. Although, it usually consist of countries located in the northern part of the continent.
Namely it is Iceland, Denmark, Norway and Sweden (Scandinavia), then Estonia, Latvia and Lithuania (Baltic countries), Finland, Belarus, Greenland and also Ireland, the Isle of Man, the United Kingdom and the Faroe Islands as well as the northern part of Germany and the northern part of Poland (because they spread across a vast area). The inclusion of various part, however, depends always on the definition.
Coming from the historical point of view, as Northern Europe were considered all areas further from the Mediterranean (formally Roman Empire) including for example Germany and Austria and it also used to be described as a mythical place far north.
That hierarchy also included the Central European region as we know today. Looking for the geographical distribution, the region of Northern Europe spreads across the Scandinavian Peninsula, Jutland Peninsula, the Baltic plain and the offshore parts north of the mainland (both smaller islands and island nations).
The areas far northwest were created by the volcanic activity (Iceland for instance). The Scandinavian part is defined around the Scandinavian Mountains and eventually the Baltic plain is a large plain area containing four countries (Finland, Estonia, Lithuania and Latvia).
Thanks to the close location to the ocean, the whole region is being affected by the Gulf Stream, influencing the overall climate. The climate of the region goes from maritime in the south to subarctic and arctic climate further north with areas of temperate and continental climate on the east.
Coming hand in hand with the various climate conditions, the fauna and flora also varies depending on the average temperature and weather conditions. High mountain peaks are mostly covered by tundra, central areas have more forests. Some countries located further north are known to have relatively cold winters with some extreme temperatures below zero.
Low temperatures although does not seem to inhibit the overall development of their inhabitants. Countries in Northern Europe in general belong to one of the most developed economies, having a high quality of life.