Europeans love to magnify even the smallest difference between neighboring countries and in northern Europe, the words "Scandinavian" and "Nordic" are not as interchangeable as you may think. If you ever call a Finn or Icelander Scandinavian, it's likely that you will be corrected and given a brief history lesson. Knowing the difference between the terms Scandinavian and Nordic is a hard distinction to make for anyone that is not a resident of these countries, so it's important to go back to the basics to clarify each expression.
In short, Iceland, Norway, Sweden, Finland, and Denmark are all Nordic countries with Scandinavian roots, but typically, you will only find Danes, Norwegians, and Swedes referring to themselves as Scandinavian.
Location of Scandinavia
Geographically speaking, the Scandinavian peninsula is the area shared Norway, Sweden, and a part of northern Finland. From this perspective, the Scandinavian countries would, therefore, include only Norway, Sweden, and Denmark. However, culturally and historically, the north of Europe has been the political playground of the kingdoms of those three countries with Finland once being a part of the Kingdom of Sweden, and Iceland once belonging to Denmark. Therefore, you can see why so many non-Scandinavians naturally connect Scandinavia to Sweden, Norway, Denmark, Finland, and Iceland.
Linguistically, Swedish, Norwegian, and Danish have a common word called skandinavien, which refers to the ancient territories of the Norsemen: Norway, Sweden, and Denmark. This definition is considered to be the most commonly accepted definition of Scandinavia at the present time, but can easily change as you travel across different regions.
The Nordic Countries
Adding to this state of linguistic and geographical confusion, the French invented the term le pays Nordiques or "Nordic Countries." This has become a common term to bring together all five of the northern European countries under the same umbrella and is accepted by all five countries.
The Baltic Countries and Greenland
The Baltic countries are the three young Baltic republics of Estonia, Latvia, and Lithuania. Greenland is a territory which is closer to America than to Europe but belongs politically to the kingdom of Denmark. Neither the Baltic countries nor Greenland is considered Scandinavian or Nordic.
However, there is a close relationship between the Nordic countries and the Baltics and Greenland. The Baltic republics have been strongly influenced, both culturally and historically, by the Scandinavian countries and the same applies to a part of Greenland's historical and cultural heritage.