Parallel computing is a type of computing in which one computer or multiple computers in a network carry out many calculations or processes simultaneously. Although the terms parallel computing and distributed computing are often used interchangeably, they have some differences.
Parallel computing vs. distributed computing
Parallel computing is a particularly tightly coupled form of distributed computing. In parallel processing, all processors have access to shared memory for exchanging information between them. On the other hand, in distributed processing, each processor has private memory (distributed memory). Processors use message passing to exchange information.