Typically a horizontal-axis bobbin. So one that doesn't have a drop-in bobbin, but one you have to put in a bobbin case, then click into place from the side.
You explained it much better. I did see where the search pulled up about the different bobbin positions as well as places to purchase a Janome, but I didn't connect the bobbin position to the DB Hook until you mentioned it. My tired brain just wondered why that was coming up in my search for a DH Hook. I have a horizontal-axis bobbin on my Babylock Accomplish, so the feet I want I think will work with my machine. Thank you.