DB, or database, is a structured collection of data that allows for easy access, management, and updating. It is commonly used in various applications, from websites to business systems, to store information such as customer records, inventory, and transaction details. There are different types of databases, including relational databases, which organize data into tables, and NoSQL databases, which handle unstructured data. Popular database management systems include MySQL, PostgreSQL, and MongoDB, each offering unique features to suit different needs.