What is relational database?

Oracle RDBMS

Database is a place where you store your data, like text file, spreadsheet, and further more relational database.

What make relational database different from the others is that, it uses logical tables to store data, and users need to interact with relational database using SQL (Structured Query Language).

For example if you create a program that store data in a text file, you need to play around with the file format or structure, then direct read from and write into the text file. While if you're using relational database, you need to deal with tables and issue SQL statement to do anything.

Another difference between relational database with others is that, it needs a DBMS (Database Management System) in order to work. All the SQL statement you issued need to go through the middle man DBMS.

That's where server come into the picture. Normally people will install DBMS and database (aware that it is 2 different entities, since you can install DBMS without any database) into a server and let users to access through client tools, website or customized programs.