Slots Volunteered vs. Unique Volunteers
From the Volunteers / Summary screen, you can see the summary of your currently Active Volunteer forms as well as the number of Slots Volunteered and Unique Volunteers for each form.
1) Slots Volunteered shows you the number of volunteer opportunities or volunteer slots that have been filled on each form.
2) Unique Volunteers shows you the number of people that have volunteered on that form. Clicking the blue number presents you with a list of the unique volunteers. It does not duplicate the name on the list if a person signed up for more than one volunteer slot.
So, in the example below, 21 people have signed up for a total of 51 volunteer opportunity slots on the Volunteer Opportunities form.