A triathlon simply refers to a swim, followed by a bike ride, followed by a run. It can be short (Sprint), medium (Olympic) or long (Iron).
People ask me if I'm doing the "real" Ironman in Kona. That is the World Championship Ironman. No, I'm not doing that one. You have to qualify. It's kinda like asking someone who is running a 5K if they're going to the Olympics. No, but it doesn't make it any less real. It's the same distance, the same struggle, and the same pride. I would like to do the Kona IM someday, but I'm not ready to commit to that level of training right now. So, yes, I'm doing the "REAL" Ironman. In Coeur d'Alene.
The IM I'm competing in is the Coeur d'Alene IM. It's part of the M-dot series of races. These are very well-organized and are considered to be qualifiers for the World Championship IM in Kona. So, if you win your age group in CDA, you qualify for Kona. The pro triathletes compete in the M-dot races. There are other Iron-distance tris, but they tend to be smaller and less organized.