Local Access and Transport Area -- but you could have learned that from Google.
This goes back to the days when Long Distance really meant something.
As a part of the AT&T breakup oh so many years ago and the introduction of competitive long distance, the country was divided up into a bunch of small areas. The local operating company was permitted to handle calls within the LATA, but had to hand the call off to a long distance company for calls outside the LATA.
Although LATAs had number similar to area codes, there was no correlation. In low density areas (like North Dakota), the LATA and area code covered the same territory. In high density areas an single area code could have manay LATAs.
While LATAs almost certainly still exist on the books, the rules changed a few years ago to allow local operating companies into the long distance business. I'm not sure LATAs have any meaningful significance anymore.