A DataReader is a component in programming that allows developers to read data from a data source, such as a database, in a fast and efficient manner. It provides a way to retrieve data in a forward-only, read-only stream, which means that once data is read, it cannot be revisited. This makes it suitable for scenarios where large amounts of data need to be processed quickly without the overhead of storing it in memory. Typically used in conjunction with technologies like ADO.NET in the Microsoft .NET framework, a DataReader can handle various data types and is often employed in applications that require real-time data access. It is particularly useful for executing queries and retrieving results from databases like SQL Server or MySQL.