Hi Joe,

Link Popularity is just the number and quality of links that you have pointing to your website from other websites.

A quick way to see how many backlinks you have is to use this free tool:
Link Popularity Check - Marketleap Search Engine Marketing Tools

If you have researched your keywords and optimized your site, then increasing your link popularity will make a big difference to where you are ranked in the search engines.

Cheers,
Suzanne