It stands for "Non-Passive Activity".
"Pub 925, page 4 "Activities That Are Not Passive Activities"-
The following are not passive activities:
- (3) The rental of a dwelling unit that you also used for personal
purposes during the year for more than the greater of 14 days or 10% of
the number of days during the year that the home was rented at a fair
rental."
Please see the whole discussion here at this Intuit-related website - https://accountants-community.intuit.com/articles/1612060-schedule-e-page-1-npa-appears-on-line-26
