The Overview tab lets you see the overall performance of your sequence. The same stats can be seen per campaign under "current tasks".
Contacts enriched are the number of prospects found and enriched that match your campaigns ideal targeting profile.
Contacted is the number of unique contacts contacted in campaigns. As contacts begin to move on to subsequent steps this number tends to rise.
Delivery rate is calculated by taking:
the total number of bounces / total number of emails sent
Number of opened emails from unique contacts. The Open rate is calculated on the basis of the number of Contacted.
total number of opens / total number of unique contacted
Number of replied contacts. The Reply rate is calculated based on the number of Contacted.
total number of replies / total number of unique contacted
Total number of conversations started from campaigns based on the classification of the response which are "interested", "Objection", "Forwarded" or "Not Now".