A database is a collection of information that is organized and maintained so that it can easily be accessed, managed, and updated. For example, in the hotel industry, a database is there to manage the availability of rooms in a hotel. Once they have one in their system they can easily have the insight of how many and which rooms are available. Every line of business needs to have a database of their work in order to function easier. In one view, databases can be classified according to types of content: bibliographic, full-text, numeric, and images.
A bibliographic database consists of collections of references of literature, magazines, newspapers, books etc. Basically everything published in a written form. It is different than library catalogues, because in the bibliographic database certain subjects are described, articles for example. You can find what you need by simply using keywords, terms or abstracts.
A full text database is very different to the bibliographical one. It offers complete texts of books, magazines, newspapers, journals etc.
A numerical database is providing data about anything that is measurable. It is always presented in a numerical form. One example of the numerical database would be how many people visited last nights concert.
An image database represents an optically formed reproduction of a person or thing.