“Freestyle” is a term used for competitive swimming. In theory, it means a swimmer can swim whatever stroke she desires. In practicality, it means crawl, which is the fastest stroke.

But this is not entirely true. In the Medley Relay (back, breast, fly, free) and the Individual Medley (fly, back, breast, free) events, “freestyle” means “a fourth stroke” other than the first three.

As a referee, I always instructed competitors to swim, not freestyle, but a fourth stroke.

It can prove tricky. In the 2015 World Championships, one swimmer began the fourth leg of the Individual Medley with a series of dolphin butterfly kicks on his back.

Since this essentially repeats the second leg, the International Swimming Federation (FINA) clarified what is now referred to as the Lochte Rule. Such kicks are allowable now only for backstroke push-offs or in a freestyle event, but not on the final IM leg.

From the above, a corollary question comes up: Why is crawl stroke the fastest?

Swimming the crawl is fastest because it involves a continuous propulsive force from alternating arms and simultaneous kicking.

In the butterfly stroke, which is essentially a double-arm crawl, there is a slight period of non-propulsion while both arms are recovering over the water.

In the back crawl the propulsive force is created farther from the midline of the body than in the front crawl. This means that it creates a small rotational force that detracts from an otherwise purely forward thrust.

Breaststroke is the slowest of the usual four competitive strokes. This is because of increased resistance caused by a greater bend of the knees and an underwater arm recovery.

However, with rule changes and better training, world-class breaststrokers are now swimming times that only freestyle swimmers were able to achieve some years ago.

Another corollary question: Does “freestyle” mean a swimmer can touch the bottom during a race? While a competitor must swim a legal stroke between the walls, one can rest at the end and even stand on the bottom (and drink or snack, I suppose) before resuming the race.

This can be comforting for a swimmer who is about to swim a long butterfly race for the first time. It’s certainly not fast. It might lack sportsmanship and earn opponents’ derision, but it’s legal.

Dr. Bob Colyer of Bluffton is an actively retired college professor, coach and author of “Swim Better: A Guide to Greater Efficiency for Swimmers & Instructors,” directed primarily to non-competitors. bobcolyer@yahoo.com