A network partition is a division of a computer network into relatively independent subnets, either by design, to optimize them separately, or due to the failure of network devices.
Distributed software must be designed to be partition-tolerant, that is, even after the network is partitioned, it still works correctly.
For example, in a network with multiple subnets where nodes A and B are located in one subnet and nodes C and D are in another, a partition occurs if the network switch device between the two subnets fails.
The CAP theorem is based on three trade-offs: consistency, availability, and partition tolerance.
Partition tolerance, in this context, means the ability of a data processing system to continue processing data even if a network partition causes communication errors between subsystems.