A database is an organized collection of structured information, or data, typically stored electronically in a computer system. It is usually controlled by a database management system (DBMS). Together, the data and the DBMS, along with the applications that are associated with them, are referred to as a database system, often shortened to just database.
Most databases use Structured Query Language (SQL) for writing and querying data.

SQL is a standard language for storing, manipulating and retrieving data in relational databases. SQL was first developed at IBM in the 1970s with Oracle as a major contributor, which led to implementation of the SQL ANSI standard, SQL has spurred many extensions from companies such as IBM, Oracle, and Microsoft. Although SQL is still widely used today, new programming languages are beginning to appear

1.Flat Files (1970s-1990s) : Flat files database is a database that stores information in a single file or table. In text file, every line contains one record where fields either have fixed length or they are separated by commas, whitespaces, tabs or any records and they cannot contain multiple tables as well.

2.Hierarchical (1970s-1990s) : As the name indicates, hierarchical database contains data in a hierarchically-arranged data. More Perceptively it can parent can have many children but one child can only have one parent i. e.,; one-to-many relationship. Its hierarchical structure contains levels or segments which are equivalent to the file system’s record type.

3.Network database (1970s -1990s) : The inventor of network model is Charles Bachmann. Unlike hierarchical database model, network database allows multiple parent and child relationships i. e., it maintains many-to many relationship. Network database is basically a graph structure. The network database model was created to achieve three main objectives:

a. To represent complex data relationship more effectively
b. To improve the performance of the database.
c. To improve a database standard.

4.Realationl database (1980s-present) : Relationship database model was proposed by E. F. Codd. After the hierarchical and network model the birth of this model was huge step ahead. It allows the entities to be related through a common attribute. In the table there are alternative keys. This property makes this model extremely flexible.

5.Object – oriented database (1990s -present) : Object-Oriented database management system is that database system in which the data or information is presented in the form of objects, much like in object-Oriented programming language. Furthermore, object oriented DBMS also facilitate the user by offering transportation support, language for various queries, and indexing options.

6. Object- relationship database (1990s-present) : Defined in simple teams, an object relationship database management system displays a modified object- oriented user- display over the already implemented relationship database management system. When various software interact with this modified- database management system, they will customarily operate in a manner such that data is assumed to be saved as objects.

There are many different types of databases. The best database for a specific organization depends on how the organization intends to use the data.

• Relational databases: Relational databases became dominant in the 1980s. Items in a relational database are organized as a set of tables with columns and rows. Relational database technology provides the most efficient and flexible way to access structured information.
• Object-oriented databases: Information in an object-oriented database is represented in the form of objects, as in object-oriented programming.
• Distributed databases: A distributed database consists of two or more files located in different sites. The database may be stored on multiple computers, located in the same physical location, or scattered over different networks.
• Data warehouses: A central repository for data, a data warehouse is a type of database specifically designed for fast query and analysis.
• NoSQL databases: A NoSQL, or nonrelational database, allows unstructured and semistructured data to be stored and manipulated (in contrast to a relational database, which defines how all data inserted into the database must be composed). NoSQL databases grew popular as web applications became more common and more complex.
• Graph databases: A graph database stores data in terms of entities and the relationships between entities.
• OLTP databases: An OLTP database is a speedy, analytic database designed for large numbers of transactions performed by multiple users.

For more info: https://www.oracle.com/in/database/what-is-database/#relational