Sitecore is a content management system and a website development environment. Sitecore is built on top of the Microsoft.NET foundation and supports everything that the Microsoft.NET platform supports. Sitecore also leverages many standard technologies, such as XML, XSLT, XPATH and other technologies from W3C and others. Sitecore takes content stored in a data source and dynamically transforms it into web pages.
In Sitecore, developers create templates which are similar to relational database table schemas. A template defines the fields associated with a set of items. An item is like a relational database record and a field is like a relational database column.
However, the difference between Sitecore storage and relational databases is, Sitecore rather than storing items in tables, organizes items into a hierarchy called the content tree. The content tree is similar to the Windows file system. The main difference is that the Windows file system tree is made up of folders which may contain other folders and/or documents containing data; whereas the Sitecore content tree is made up of items which contain data but can also act like folders and have sub-items.