Off-Page SEO are the factors that influence the search engine ranking of your website that are not in your direct (immediate) control.

Items that fall under the umbrella term of Off-Page SEO:

Quite obviously a digital marketer can influence off-page SEO, so it’s not that they are completely out of their control, it’s that the factors require external environmental impact.

In contract, On-Page SEO refers to those items which are in the control of the webmaster or digital marketer.

For more details on what Off-Page SEO is, consult this article by Joshua Hardwick:
Off-Page SEO: What It Is and How To Crack It