Brewer's theorem

Etymology
Named after computer scientist Eric Brewer.

Proper noun

 * 1)  A theorem stating that it is impossible for a distributed data store to simultaneously provide more than two of three guarantees: consistency (every read receives the most recent write or an error), availability (every request receives a non-error response, without the guarantee that it contains the most recent write), and partition tolerance (the system continues to operate despite an arbitrary number of messages being dropped or delayed between nodes).