So what are all these terms means?
This information can’t be cached to disk, so it must stay in RAM. The amount depends on what applications you are using.
This information is currently in RAM and actively being used.
This information is no longer being used and has been cached to disk, but it will remain in RAM until another application needs the space. Leaving this information in RAM is to your advantage if you (or a client of your computer) come back to it later.
This memory is not being used.
More info can be found in: