Short definition
NAP stands for Name, Address, and Phone — the three business identifiers Google compares across the web to verify a local business is real and consistent.
In depth
NAP consistency is foundational local-SEO hygiene. Google cross-references your GBP NAP against citations on Yelp, Apple Maps, Bing, BBB, industry directories, and your own website. Inconsistencies (an old address on a directory, a tracking number on Yelp) erode trust and rankings. The fix is a citation audit followed by systematic cleanup. Some businesses also add NAP+W (with website URL) and NAP+H (with hours) for more complete signals.
Example
A dentist with two old addresses across 30 directories cleans them up and sees map-pack rankings improve in six weeks without any new content.