Niggas Per Minute (abbreviated as "NPM") is a stat used to measure song lyrics. The NPM is the average amount of times the word "nigga" (or it's derivations: "nigger", "nig", etc.) is used per minute in a song.
For example: The song "344 Words" by Young Blaze is about 1 minute 45 seconds. He uses the word "nigga" 22 times. The NPM for "344 Words" is 15.17
Jason: Yo have you heard that new Meek Millz song? Shit's a banger!
Kyle: Yeah, but what's the Niggas Per Minute? Probably around like 10, he's no lyricist. Eminem got by fine with a steady 0 NPM throughout all his songs