SQL is a language used to manage and interact with most relational databases so it is used often to describe relational databases. There are many tables in a relational database, each is very much like an excel tab. The excel spreadsheet can have many tabs relating to each other. So kinda similar. However a relational database is better defined, more functions and forced relationships, and most important space efficenct. Excel takes probably 100-1000 times more space, and that is best case.