There is no difference, other than the intent of the person being described.
A viking was a trader who would sometimes raid small villages or other boats. They took advantage of a situation if it presented itself. Vikings were never full time vikings, they were either warriors during peacetime, or other karls (freemen) who would be lead by a Jarl (someone of noble birth, usually the second son of a king or chieftain). A trader would of course be a full time trader, someone who made a living off trade. Vikings made their living by other means. Most vikings were actually farmers, including the peace-time warriors.
A Viking.
They are the same thing. The Vikings would trade or plunder.
The Viking are the Norse
Norse
Old Norse refers to the language. Norse refers to the people.
Some call it the Norse Religion, Viking Mythology, and the Viking Religion, but the most correct is Norse Mythology.
Yes, the Vikings were the Norse "pirates".
A story of the lore of the Norse/Viking people.
A Norse saga is a true story, written about 1000 years ago in gammel-norsk or icelandic. Many of these are about viking, and are referred to as viking sagas. It is important to note that viking is a verb : it referred to what the people did, rather than who they were. Viking was a form of piracy, where people went to see in good, seaworthy boats, capable of long voyages. The essential difference between viking and piracy was that the attacks were not on other ships but on villages or towns on, or close to, the seashore. All the Norse sagas are worth reading, whether the viking content is dominant or minimal.
The Vikings spoke Old Norse and the Old Norse word for beast is dýr.
Most Vikings followed Norse Paganism throughout most of the Viking Age, but they slowly converted to Christianity between the 8th and the 12th century.
The word "viking" comes from "vikingr".