It's said that Trent Reznor chose the name simply because it had a simple but memorable abbreviation, and that it didn't have any literal meaning. People though assume that it could be anything from the spikes used to crucify Jesus to the blades on Freddy Krueger's glove.
I have heard also that he chose it because it abbreviated easily and he designed the logo. What many don't realize is that NIN is not a band, it is Trent Reznor. He assembles a touring band after a major studio release. I didn't know this for years until my son informed me.