Standard and Network Edition: You require one licence per installation. If you share an installation (e.g. on a server) then you require one licence per user. You can search/analyse any number of servers with each installation, limited only by the performance and capacity of your PC/network.
Enterprise Edition: You must buy one Base Licence and any number of additional Client Access Licenses (CALs). Each Base Licence includes 5 CALs. You require one CAL for each installation of SPACEWatch Pro Enterprise Edition on a PC or server. If you share an installation e.g. on a server then you require one Client Licence per user. For each server scanned you need a CAL. For example, with the 5 CALs that come with the Base Licence you could install SPACEWatch Pro Enterprise Edition on one PC (= 1 CAL) and scan data from up to 4 remote systems (= 4 CALs). You can buy additional 5-packs and 20-packs of CALs to fit your needs - or a Site Licence with unlimited CALs that you can apply at any sites used by your organisation within one country.