Your billing page is where you can view your current billing tier and plan details, overlap units and partner-facing users (check out our pricing page for more details on the tiers).
To get to the billing page, go to the user menu in the top right (your company's logo), and click on "Billing".
Overlap units are the number of unique records that are receiving data from each of your partners.
For example, if you have one account that overlaps with (and is receiving data from) three of your partners, that counts as 3 overlap units. The number of populations that account is in, for both you and your partner, is irrelevant.
The overlaps table will show you how many overlaps you have with each partner.
Note: If you are partnered with Crossbeam on Crossbeam (so meta), overlaps with Crossbeam will not go towards your quota, and will look like Michael Scott Paper Co. in the screenshot above.
Overlap units are updated daily. You can see when they were last updated on the bottom left of the billing block: