The .accdb file extension is the default file format for databases created with Microsoft Access, a relational database management system (RDBMS) from Microsoft. It replaced the older .mdb format starting with Access 2007. ACCDB files store database structures, including tables, queries, forms, reports, macros, and modules (VBA code). They can contain data itself, or link to data stored in other file formats or databases. The ACCDB format supports more advanced features compared to the older MDB format, such as multi-valued fields, attachment fields, and integration with SharePoint. It also offers improved security and encryption capabilities. ACCDB files are designed to be used with Microsoft Access and are not directly compatible with other database systems without conversion or specific drivers. They are commonly used for small to medium-sized database applications, such as managing customer information, inventory, or order tracking. The file format is proprietary to Microsoft.