Reserve is quite similar to a minable amount. I.e. if we use the term reserve, Bitcoin now has 21 mil reserve (if half of them are already mined), which can be mined in the future. The difference of reserve is that reserve can either increase or decrease. So basically you're right. It's not in circulation, it is not available to the public for now.
Thanks for MUSE update @Gliss
But I see the reserve is misunderstood. It tells us maximum hard cap of MUSE supply, so the maximum supply of MUSE can be 2 bil (1.5 bil of total supply + 500 mil of reserve)
Therefore, the current available supply should be adjusted to 1,353,319,794, not 853,319,794.
Here's an infographic of BitShares funding system including reserve
https://bitshares.org/technology/stakeholder-approved-project-funding/
Please correct the supply at your convenience. Again I really thank you for updating MUSE info.