what is pdo in php?

PDO stands for PHP Data Object. PDO is a set of PHP extensions that provide a core PDO class and database, specific drivers. The PDO extension can access any database which is written for the PDO driver. There are several PDO drivers available which are used for FreeTDS, Microsoft SQL Server, IBM DB2, Sybase, Oracle Call Interface, Firebird/Interbase 6 and PostgreSQL databases, etc.

It gives a lightweight, vendor-neutral, data-access abstraction layer. Hence, no matter what database we use, the function to issue queries and fetch data will be the same. And, it focuses on data access abstraction instead of database abstraction.