But the term has a very specific technical meaning [1], not just 'very fast'. This is analogous to when people say that 'NP-complete' is synonymous with 'very hard'. If I posted a problem to HN that I solved and that I found very difficult, but was not np-complete, and said "look at my solution to this np-complete problem" people would certainly (hopefully) complain.
1. http://en.wikipedia.org/wiki/Real-time_computing