It is often used in a context like ランチバイキング and ケーキバイキング. If you know Katakana, I don’t think it is too hard to figure it out to be “Viking”, but why “Viking” has something to do with “lunch” and/or “cake”? I’m not sure.
バイキング is the same as 食べ放題（たべほうだい）, which means "all you can eat." Sometimes, it is also called ブッフェ from the French word, "buffet," but the word バイキング is more commonly used.
If each member of your family wishes to have different things for lunch or dinner, バイキング would be a great option for you. Especially at lunch time, many バイキング restaurants have quite a good deal!
Drinks can be included but not always. Some places have a time limit as well. So check those before you decide to sit down!