NAP stands for Name, Address, Phone - and "NAP consistency" means your business is listed identically across every directory and platform (Google, Yelp, Facebook, industry directories). Inconsistent listings - a slightly different phone number on one site, an old address on another - can confuse both search engines and homeowners trying to verify you're legitimate.
The fix is a one-time cleanup: search your business name across major directories, correct any mismatches, and make sure new listings always use the exact same formatting going forward. It's unglamorous work, but it's a real, checkable factor in how much Google trusts your local listing.