What is the difference between a process and a thread? When would you use one instead of the other?

A process is an independent execution unit with its own address space, resources, and memory. A thread is a lightweight execution unit within a process that shares memory and resources with other threads of the same process.

Main differences:

• Processes are isolated from each other, threads are not.
• Creating a process is more resource- and time-consuming than creating a thread.
• Threads are convenient for parallel execution of tasks that require shared access to data.

When to use:

• Processes — when isolation is needed, for example, for security or stability (an error in one process will not affect another).
• Threads — for parallel processing within a single program, when it is necessary to share state and data.

In Java, for example, multithreading is used to improve application performance and responsiveness, while processes are used to run separate applications or services.