There are already several
definitions for this term on here, but all of them are wrong.
I think people must be confusing "hard fart" with "dense fart", and those terms are not the same thing.
A "hard fart" or "hard gas" is a medical term, something you might tell your doctor or your doctor may ask you about. A hard fart is a painful fart that sometimes has to be squeezed out to relieve pressure in the bowels as a result of
constipation. You will discuss this with your doctor as a symptom of
constipation. Usually, there is no defecation associated with a hard fart because of an underlying constipation issue. Sometimes a small amount of solid particles or "fecal debris" may pass along with this fart leaving skid marks, but this is not the same as a "shart".
Conversely, a "dense fart" comes about as a result of a diarrhea issue, usually a precursor to blowing mud. Hard farts are a precursor to having a painful, dry bowel movement sometime (
often days) later.