A database is an organized collection of data. The data are typically organized to model relevant aspects of reality (for example, the availability of rooms in hotels, cancel seats for a airline reservation, register a new tudent into a school’s English class), in a way that supports processes requiring this information (for example, finding a hotel with vacancies, releasing reserved seats, entering new student details into school name list and under English subject class respectively). 1

Databases are incredibly prevalent — they underlie technology used by most people every day if not every hour. Databases reside behind a huge fraction of websites; they’re a crucial component of telecommunications systems, banking systems, video games, and just about any other software system or electronic device that maintains some amount of persistent information. In addition to persistence, database systems provide a number of other properties that make them exceptionally useful and convenient: reliability, efficiency, scalability, concurrency control, data abstractions, and high-level query languages. Databases are so ubiquitous and important that computer science graduates frequently cite their database class as the one most useful to them in their industry or graduate-school careers. 2

The term database should not be confused with Database Management System (DBMS). A DBMS is the system software used to create and manage databases and provide users and applications with access to the database. A database is to a DBMS as a document is to a Word Processor.

There are many database systems developed and available for programmers/end users with their own languages syntaxes. These languages are to perform data manipulation on the database using a DML (Data Manipulation Language). The most widely used DML language is SQL. Below are listed a few out of the many DBMSs found on the market today,

• MySQL
• PostgreSQL
• Oracle
• SQLite
• SQL Server
• Sybase

Along with the improvement of database technology there are many criteria to question the usage or selection of a database in terms of,

• design
• managing a database
• retrieving data from database
• importing data into the database
• tuning of a database
• database security
• Database connections

Some of the above references are given mainly from wiki. Let your imagination run wild by searching for relevant articles further!

NOTE: The content of this tag was originally posted at StackOverflow.com