“Modern Triathlon” or “Triathle” is a sub-sport of Modern Pentathlon, an Olympic sport since 1912.
It is being promoted by UIPM, which is the international body behind the sport (just like ITU).
There are actually three sub-sports of Modern Pentathlon–Triathle, Biathle, and Laser-Run. (See my descriptions below for the gist of each one.)
I just got back from the UIPM Triathle / Biathle World Championships, which were held in St. Petersburg, FL, last weekend. I took my three kids there. We competed at the elite level for Team USA and had some incredible results! (See some awesome photos of the event here: https://www.uipmworld.org/photo-gallery.)
As many who know me from this forum know, I am a long-time aquathlete and triathlete, having competed at ITU Aquathlon Worlds in 2017, Ironman Lake Tahoe in 2013 (the first one), many half Ironman races, and all kinds of multi-sport races in between. Well, I have to say, I’m totally hooked on all of these new sub-sports of Modern Pentathlon.
The sub-sports consist of multiple sequences of swimming, running, and laser-pistol shooting. Think Biathlon (the winter Olympic sport that combines cross-country skiing and rifle shooting), except at sprint (or middle) running distances and using a pistol instead of a rifle. Important note here: the pistol is basically a completely safe trigger-activated “class 1” laser (like a laser pointer) with a gun-shaped housing. This is a change that was made to the sport of Modern Pentathlon starting with the 2012 Olympic Games. (See, e.g., https://www.wired.com/...thlon-laser-pistols/.)
Biathle–multiple sequences of running and swimming, with distances varying by division (e.g., the masters 40+ division at the World Championship was a 1200-meter run, a 100-meter swim, and a 1200-meter run).
Triathle–multiple sequences of running, swimming, and laser pistol shooting, with distances of run, swim, and target varying by division (e.g., the masters 40+ division at the World Championships was 4 x 600-meter run, 5 hits at a 10-meter target, and a 100-meter swim).
Laser-Run–multiple sequences of running and laser-pistol shooting, with distances of run and target varying by division (e.g., the “open” division does 4 x 800 meters with 5 hits at a 10-meter target). Laser-Run is a stand-alone event, but it is also the “combined” event that concludes the competition of a Modern Pentathlon. It will likely next be seen and have international exposure at the Tokyo 2020 Olympic Games.
None of these sub-sports has gotten much traction in the U.S., but they seem to be getting more popular in other countries. There were about 600 participants at the World Championships, but very few from the U.S.! At the World Championships, the dominant countries included Great Britain, Egypt, Guatamala, and South Africa. There were 34 countries represented.
Which brings me to one of the reasons I’m making this post. I’m putting together an unusual multi-sport event that will be held at Westmont High School in Campbell, CA, on November 24, 2019 (three weeks from today). It’s going to be a combined all-comer track meet and laser-run, sponsored by my running club (Wolfpack Running Club, a non-profit organization). The track events will be sanctioned by USATF and the laser-run events will be sanctioned by USA Pentathlon. (See http://www.dashnzap.com.)
I really want to make this event a success and would greatly appreciate it if you could help me get the word out. Before you know it, Modern Triathlon might just take the place of the ancient triathlon we have been discussing ad naseum on this forum for years . . . 
K_Man