In Indonesian (and Malay) the word parang just describes the fact that it's a big knife ( a bit like saying "jungle knife") A Golok is a specific style of parang - usually slightly shorter with a broader tip. It (I believe) originated in Java though there are many different similar styles from all over S.E. Asia. It is more useful in dense secondary jungle where you may not get a long swing at whatever you're trying to cut if you use a longer blade. The tip heavy Golok gives a lot of cutting power for a shorter blade length - it has disadvantages when it comes to reach though.
All of the above is my opinion - at least it was when I wrote it. It might have changed by now though 'cos it's not all black and white.