The definition of a "client" or "asset" in Lansweeper is a machine scanned by Lansweeper or a machine that was manually added to the database. This can be a Linux, Unix, Mac or Windows computer, VMware server or other network device (printer, switch…). You can view your current client count in the Configuration/Scanning Setup/Database Scripts section of the Lansweeper web console.
Monitors do not count as licensed assets. You can check the actual number of licensed assets in the section Configuration/Your license.
Only the Standard versions (250 clients / 750 clients) are limited to respectively 250 and 750 licensed assets. All other license types have no limitation on the number of assets.