For the purposes of our licensing, we count one "site" as one installation of Wordpress & OptimizePress. So if you have a site where you have installed Wordpress and OptimizePress, whether on a subdomain or main domain, that will require one license
If you have further subdomains attached to a multi-site on the same main domain, these will each require their own license.
Remember: You can build an unlimited number of PAGES on each site that you install OptimizePress (landing pages, sales pages, membership pages etc) - your only limitation is your hosting webspace and bandwidth which is set by your chosen hosting company.
If you have any further questions about our licensing for OptimizePress please search the knowledgebase or contact our team using the link below