DNP

DNP is a three-letter abbreviation which can stand for:

2,4-Dinitrophenol a small organic molecule
Dynamic Nuclear Polarisation a technique used in NMR spectroscopy
"Did Not Play" a notation used in a basketball box score
Distributed Network Protocol (DNP3) a protocol used in SCADA systems between communicating RTU's and IED's
Duty Not Paid, in the context of cigarette smuggling