The historical mentions are the ones that you'll have in-depth data access to. You can receive email alerts on these type of mentions, you can run detailed reports, and you will have fully managing capacities on them.
The Projects consume the Historical Mentions and these are the total number of mentions collected over time in your account (under the total projects). These are historical mentions and they don't reset. They are the total of mentions in an account at a moment.
Check the image below to see where you can find the total number of historical mention in your project.
To find the total number of historical mentions consumed in your account you can go to the Account Settings >> Projects
The instant mentions are the ones that you will consume while using BrandMentions' Quick Research Tool. You can search for any brand or topic and get instant mention results for any country or language you are interested in, on a time frame from 24hours to 30 days.
Instant Mentions are only provided to you in the interface with no possibility of tracking and getting alerts based on them. They are used for quick research purposes such as quickly checking a keyword, company or competitor that you just want to see how is doing. Instant Mentions are volatile and they are not stored/saved in your account. You can look at the Quick Research Tool usage like a search engine for mentions.
Instant Mentions reset every month while historical mentions don't reset.
Historical Mentions are the total number of mentions stored in your account.