Buffets and sideboards are diferent words but they represent the same thing. For the Frenchs a buffet is a small sideboard used essentially for storing dishes. Both terms are often used, but regardless of what you want to call it, buffets and sideboards can be stylish and functional additions to the dining room.
Sideboards date back to the 18th century, but nowadays trends tend to include contemporary and modern features in addition to antiques. Sometimes they inclusively mix it. The most important thing to take into account is the dining room theme, and to always trying to complement it with small details!