Stickiness refers to the time spent on the page or the high number of visited pages across multiple sessions by the same visitor or user.

What is customer stickiness?

Customer or web stickiness refers to the process of a visitor to repeatedly visit a particular site, to (re)browse multiple pages and spend more time on a site’s pages. Stickiness is often measured in the average minutes per month spent by visitors or in terms of page views.
Moreover, the stickiness can refer to:
Session stickiness that refers to the tendency of a customer (or visitor) to spend more time on a site in each site visit;
Site stickiness, or repeat usage, refers to the tendency of a customer (or visitor) to re-visit the pages multiple times over multiple sessions.

How to increase stickiness on the website?

Stickiness implies an excellent onboarding process focused on engagement and even gamification to motivate the visitors to come back on the site and stick within it. To increase stickiness for a website, the following tactics can be considered:
Create a smooth onboarding process
Provide compelling and relevant content 
Add internal links for cross-references and to keep the visitor within site for more information
Allow the user to customize its dashboard (e.g., Slack)