In Target, activity is defined on page URL and based on some qualifying criteria (audience used), we qualify for the activity. Then data under metrics Visitors/Visits is captured for all those visitors who were part of that activity.
For information on how visitors are captured in Target for an activity, refer the article New or Returning Visitor.
Visits is the count of single visitor visiting your site as a part of that activity.
In Target, if I load the page and if I qualify for the audience used for the activity, then only data is attributed to metrics.
In Analytics, there is no such qualifying criteria and data under visitors/visits are captured for all who visited the site.
There are differences in data that has been recorded by each tool, and there are reasons for this variation mentioned in the following documents:
- Understanding Expected Data Variances (Deprecated)
- Personalization, bridging the gap dealing with variance between data systems
Whereas, in Analytics, the visit is always associated with a time period, so you know whether to count a new visit if the same visitor returns to your site. A session starts when the user first arrives on your site, and ends under one of the few scenarios. For example, a visitor comes to your website, closes the browser and reopens it 5 minutes later, that would still be counted as the same visit. A unique visitor is the visitor who visits your website for the first time within specified period.
This is why if you have a Segment built in Analytics and if you were to compare the number of instances for that report with the number of instances for your Activity, it is impossible for them to ever match simply because of the way Analytics Segments currently work as dimensions/metrics used in the segment would work on the Allocation/Expiration of the variables set by the users.
For example, on a single day Site Catalyst shows unique visitors for all those who entered the site on that day. It would not count that visitor again.
Target, however, can count a visitor multiple times in one day depending on how the success metrics are set up.
For more information on minimizing the effects of inflated Visit and Visitor counts when using Analytics as a reporting source, refer the document Minimizing Inflated Visit and Visitor Counts in A4T.
Because of these wildly differing definitions, of the metrics in Analytics and Target and the algorithms being used to calculate, the difference in data occurs.