Definition of metrics

Page Views: The number of times the s.t() function was fired within the given date range.

Visits: The number of sessions within a given time period. A visit is defined as a sequence of consecutive page views without a 30-minute interval, or continuous activity for 12 hours.

Comparison of metrics

Page Views higher than Visits: This comparison is expected, as a visit commonly contains multiple page views.

Visits higher than page views: All visits contain page views, except under rare circumstances where a visit contains only custom link image requests. This anomaly is unlikely to occur unless the s.t() function is removed from your implementation and custom link tracking is solely implemented. Other than this edge-case, page views are always higher than visits. 

Additional resources