Shows the accumulated number of visits that a user has generated since from his first contact up to his last visit.
Example
A user had his first visit on February 13 and performed 3 visits in total:

The analysis for the whole time period (Feb 13 to Feb 15) would yield the following result:

The analysis for Feb 14 would yield the following result:

Using this dimension over time is normally not useful, as there is no time reference.
Example of using this dimension in a filter
- Show only data of users that performed more than three visits in their lifetime:

Similar Dimensions
URM - Customer Visits: Counts the lifetime visits of a user up to a certain point of time.
Training document Extended user-centric analyses