Berkeley DB (BDB) is a software library that provides a high-performance embedded database for key-value data. It is a widely used database engine that is known for its simplicity, reliability, and performance. Berkeley DB is written in C and provides a number of features such as support for transactions, locking, and recovery. It is used in a variety of applications such as databases, content management systems, and data storage systems. Berkeley DB is available for users to download and use in their own applications under an open source license.