“We’re saving lives, and saving a lot of them,” Mr. Glassman said. “Three hundred fifty thousand Americans are going to die next year from sitting on the couch. That’s dangerous. The TV is dangerous. Squatting isn’t.” He said he has refrained from marketing his own gym equipment because that would hurt his existing suppliers, which would be a “sin.”

In the classic 2000 essay collection “Religion and Popular Culture in America,” scholars argued that activities as diverse as “Star Trek” fandom, dieting fads and football could all constitute religions. But if anything that creates community and engenders passionate devotion can constitute religion, does the word lose all meaning? If everything is religion, then maybe nothing is.

For Joseph L. Price, who teaches religion and popular culture at Whittier College in California, the key criterion is whether a given activity establishes a worldview.

“To what extent is the worldview of the CrossFitters determined by their practices, their aspirations for the perfect body, or for the most fit male or female in the world?” Professor Price said in a recent interview. “Does their aspiration for fitness shape their view of how their world is ordered and organized?”

Using this logic, one can see how “Star Trek” fans, with their deep interest in science and cosmology, might qualify as religious. But members of a men’s breakfast club who meet weekly at a diner, by contrast, while they might derive great joy and comfort from their ritual, would not, by virtue of it, be religious.

Of course, that is just one way of answering the question of what a religion is. At the Harvard discussion with Mr. Glassman, Mr. ter Kuile, who plans a career in ministry to the “nones,” as the religiously unaffiliated are often called, offered other criteria.