RAM: Wired, active, inactive, free

Not sure which forum this goes in:

I've been watching my activity monitor to see if it's really worth running a background app which take up a lot of memory. When I run it the 'free' memory drops like a stone. The active & wired memory rises a little, and the inactive memory rises to make up the rest of the drop. A 3rd party activity monitor (iPulse) groups inactive RAM with free memory and shows this app using less than I thought.

My questions:

What is wired, active and inactive RAM?

Can inactive RAM be claimed back by another app (eg a game) which may need it?

Also, when I quit this app, only the wired and active RAM is returned to the 'free' pool. The inactive stays the same. Is this normal, or do I report it as a bug?

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