What is ground red pepper?

In most instances I've seen, in American cookbooks, "red pepper" refers to cayenne pepper or chili powder (not the spice mix designed for making chili con carne, but dried, ground chilis). It is usually spicy rather than being red bell pepper.

Edit to add: I'm talking about this type of product:

McCormic Ground red pepper

Source

The term "ground red pepper" is ambiguous in English. Things sold under that name in the US have a wide range of heats, and likely are made from multiple varieties of peppers, though I'd say they're more commonly hot things like cayenne, or other varieties with somewhat less heat.

That said, don't worry about it too much in these cases. Anything from mild paprika to cayenne would likely fit within what the authors meant, and you're not going to harm a recipe by increasing or decreasing the heat, or by using a chile powder with a slightly different flavor. Just use something (or a blend) that provides the heat level you want, and you'll be fine.

I had a red pepper spice by Astor out of Jacksonville, Florida. They are out of business, now, to my regret. Their pepper was not hot but has a very nice flavor and smell. I would use this spice without having to use salt or any other spice. It would change the smell of meat to delicious even as you sprinkled it on. I have not been able to find anything like it. It was not cayenne nor chili. Just labeled "ground red pepper". I saw on internet the same pepper by Astor "the Tin" for sale, it's very old so I probably will not bother with it. In other words, there was once a ground red pepper spice, not cayenne nor chili.

A generic bulk product labeled and called only "red pepper" is sold very cheaply in most International Markets, Asian and Chinese grocery stores in US.

It is always a very finely ground red powder sold in 500g (and much larger) clear plastic pillow shaped bags that I can never use up. (Normal label just says Brand, "Red Pepper", weight.)

I think it can be used to make the hot flavors when preparing "Chinese" dishes and I use it to add "heat" to any "Chinese Food" that was not made spicy enough.

Careful, this dry power will make you sneeze and irritates the eyes more than finely ground black pepper. Sometimes without even opening it.

It contains it's seeds and is a bit hotter than any crushed red pepper used on Italian food. (Mostly because that "crushed" is more coarsely grated flakes than any coffee grind.)

Every decade or so when it turned brown, I searched for another market that didn't exist long enough for me to get it again.

I add 1/8 teaspoon to a 1 pound skillet dinner.

So, I only buy one of the smallest packages and repack it in a canning jar or a used spice dispenser container saved and washed from something mild enough to use up. (Like Italian seasoning)

It's just crushed cayenne pepper!