A re-initial is an initial member that has downgraded to a basic membership, then re-upgraded to become a full paying member (initial) again.
Understanding re-initials is important as it will mean the lifetime value for a member will increase. The re-initial revenue associated with a member that re-upgrades can be linked back to your marketing campaigns and is likely to impact the amount you can afford to spend on acquiring a member.
In order for your campaign tracking reports to generate accurate, useful data, you must ensure the White Label Dating campaign tracking script is installed in your landing page. If you are using the WLD design tool to create your landing pages, this will already be present. If you are using a custom-built landing page, you (or your developer) will need to add this code manually.
More metric definitions can be viewed in summary here.