Find common features and differences between processes and threads from several points of view (usage, size, execution, life cycle, implementation, etc.)
Then focus (and post here) on one common feature and/or difference that you found.
Please avoid repetition of the same list of similarities and differences.
I would suggest to pick one similarity / difference and elaborate a little bit on that subject, perhaps with concrete examples on how things are done on a certain OS or another.
Examples always help understanding the topic.