Apparently, that’s called a trivet.
There are also brevets and privets. A privet is a well-defined object (although some indeterminancy surrounds the term ‘noctious’, which in some quarters, a privet is), but a ‘brevet’ has so many possible meanings you could write a book about them.
Anyway, I love it when you make something and in the process it accidentally expands your vocab.
Oh and … making felt is easy and relaxing. But you need a bit of gear, and carding wool is somewhat *less* fun.