What is microsoft sql server 2008?

A server and more precisely a database management system(DBMS) server. Even more precisely it is a SQL databse management server like Oracle, MySQL, postgresql etc. You definitely would already have known about Microsoft Access (which is not actually server) which was an older way Microsoft provided data to be stored in simple access files. Servers are however far better with lots of extra features and mainly security. It is Microsoft flagship product in the DBMS field. Biggest competitors of it includes IBM DB2 and Oracle.