Concurrent vs Parallel?

[alash3al]

This package uses pcntl_fork which uses fork(2) to create a child process based on php.net docs.

A child process means it may be executed in parallel not concurrently, Am I wrong?

[brendt]

concurrent execution - the execution of two or more computer programs by a single computer

parallel programming - This type of programming takes a problem, breaks it down into a series of smaller steps, delivers instructions, and processors execute the solutions at the same time

I'd say both definitions match? What's your interpretation of "concurrent" and "parallel" ?