What is the difference between a process and a thread?

A process is a running program with its own isolated memory space, including its own heap, stack, and code. Threads, by contrast, share the heap of their parent process but each thread maintains its own stack (typically 512KB to 1MB) and program counter. Because processes are isolated, communication between them requires inter-process communication mechanisms like pipes or sockets, whereas threads communicate directly through shared heap variables, which introduces the need for synchronization to avoid race conditions. Creating a new process is relatively expensive because the operating system must set up a new address space and associated data structures, while creating a new thread is cheap since it only requires a new stack and reuses the parent's existing resources.