Certificates/Domain you could run into through repeated re-issuance. This limit measures certificates issued for a given combination of Public Suffix + Domain (a "registered domain"). This is limited to 5 certificates per domain per week.
Is there a specific day and time in the week for the 5 certs/week limit to lift?
My understanding is that it’s within the past 7 days, or 168 hours as tlussnig wrote. Basically, it’s a floating window. Assuming that understanding is correct, the language should probably be modified to make that clearer.