They can be both frequent and rare. They are rare in the sense that the number of people directly affected by them is tiny compared to the population.

There is an injury from a lightning strikes about once a week in the US - frequent! Yet the vast majority of people will still not be struck by lightning in their lifetimes - rare!

While I do think we need to enact much stricter gun control, people touting this website about “mass shootings” always gives the outside world the idea that all of them on that list are like the Vegas concert shooting, which people think of when they hear the term “mass shooting.”

From their methodology page on how they characterize a mass shooting-

In that, the criteria are simple…if four or more people are shot or killed in a single incident, not including the shooter, that incident is categorized as a mass shooting based purely on that numerical threshold.

If you click through the incidents and read the reports, almost all are isolated incidents. Gang violence, mentally ill people murdering their family and committing suicide, other terrible things like that. Which is tragic and very much strengthens the argument about needing stricter gun control. But people keep linking that page, people go there and see a wall of reports, and assume all of them are crazed gunmen firing indiscriminately into a crowd at a shopping mall or the like. It’s not like that at all, but curating the data with their methodology and saying the details don’t matter and all mass shootings are the same as long as 4 people are injured just paints a disengenuous picture to people who don’t live here. I’ve seen plenty of people that post they refuse to visit the US because they think they’ll be randomly shot for no reason while walking down the street, which isn’t at all a normal occurance. Sadly I’m more afraid that if a cop wants to stop and talk to me that I’ll get shot much more than I am going to a festival.