Hi!
The licenses are single use, meaning they should be used on a single end product (in this case website). The exact details can be found here: https://codecanyon.net/licenses/standard
Unfortunately the vendor platform (codecanyon.net), does not offer multi-end product licenses yet. The price however is not re-curring for the product itself, so the plugin is yours forever with all the updates included in the future. I guess that justifies the single use.