Distributed Databases
According to Wikipedia:
A distributed database is a database in which data is stored across different physical locations.[^1] It may be stored in multiple computers located in the same physical location (e.g. a data centre); or maybe dispersed over a network of interconnected computers.
Cassandra
Cassandra is a distributed database that is designed to handle large amounts of data across many servers. It is preferred for its scalability and availability. There's a lot more information on it in the Cassandra document.
References
Footnotes
[^1]: www.its.bldrdoc.gov "Definition: distributed database".