A process is an independent program in execution. It has its own memory space, code, data, and system resources. Each process runs separately from others, so if one process crashes, it usually doesn't affect others. Processes are heavy to create and switching between them (context switching) takes more time and resources. A thread, on the other hand, is a smaller, lightweight unit of execution that exists within a process. Multiple threads can run within the same process, sharing the same memory and resources. Because of this shared memory, communication between threads is faster and easier compared to processes. However, this also means that if one thread crashes or misbehaves, it can potentially affect the entire process.