What are Referring IPs?
These are the IP addresses of the servers hosting those websites that include a link to your website.
Suppose, you have a website "yourwebsite.com". It gets a link from a website "example.com".
The referring IP of your website would be the IP address of the server hosting the website "example.com".
This concept is usually used to see the backlink profile of a domain. If a domain is getting backlinks from unique IP addresses, it would be considered a diverse profile.
A single IP address can host multiple domains or websites simultaneously. Many tools can help you see the IP address of a website such as Majestic Neighbourhood Checker.