NAP simply means your Business Name, Address, and Phone Number in the order. As you already know, NAP is a very important ranking factor when local SEO for your business comes in. This is because it directly affects local intent searches on Google and other search engines like Yelp. Occurrences of NAP data around the web are called citations.
It is known that out of the top 6 “Basic Ranking Factors”, 3 are related to citation quality, quantity, and consistency. The QUALITY and QUANTITY of citations of your business on directory sites (like Yelp and Manta) are a major factor when determining how you rank locally.