CMDB stands for configuration management database
CMDBs are used to keep track of the state of assets such as products, systems, software, facilities, and people as they exist at specific points in time, as well as the relationships between such assets. The maintenance of such state related information allows for things like the reconstruction of such assets, at any point in their existence, as well as for things such as impact analysis, in the cases of root cause analysis or change management.
A CMDB helps an organization understand the relationships between the components of a system and track their configurations. The CMDB is a fundamental component of the ITIL framework’s Configuration Management process. CMDB implementations often involve federation, the inclusion of data into the CMDB from other sources, such as asset management, in such a way that the source of the data retains control of the data. Federation is usually distinguished from ETL (extract, transform, load) solutions in which data is copied into the CMDB.
CMDBs can be used for many things, including but not limited to business intelligence, software and hardware builds, and impact analysis for both change management and incident management.
In the context of ITIL the use of CMDBs as part of infrastructure operations and support. The CMDB represents the authorized configuration of the significant components of the IT environment.
ref: https://en.wikipedia.org/wiki/Configuration_management_database