With each plan, you are assigned to a total number of URLs, Keywords, Site Audit pages, and white-label reports that you can add and track within your account.
The total number of keywords, URLs, Site Audit pages, and White-label reports is counted account-wide, and not URL-wide.
Let's take this plan as an example:
Based on this example above, you can add all 1000 keywords in one single URL, or you can track 200 URLs and add only 50 keywords in each of them - you're free to play around with the limit however you like, as long as the total of keywords does not exceed 1000 account-wide.
Note: Each keyword that you add with its own settings (location, language, device, search engine) counts as an individual keyword.