If you’re a male, a protruding bump at the back of the heel bone is called Haglund’s Deformity. If you’re a female, it’s called a Pump Bump. They’re both the same thing and represent excess bone forming at the back of the heel, usually because of lower leg alignment. Essentially, what happens is the the heel bone fishtails across the back of the shoe, with repetitive friction causing excess bone to form.
For most of us an enlarged Haglund’s or Pump Bump is harmless, but for my patient, seemingly out of nowhere, the bump started to become increasingly red and painful. Dress loafers were not the culprit, so I asked to see his workout shoes and this is what I discovered.
The inside heel area of his shoe was not only excessively worn but the plastic counter had actually cracked, essentially rubbing his heel bone raw.
The solution? New shoes with careful monitoring of wear and possibly even a shoe with a soft heel counter, depending on future wear.
Dr. Jenny Sanders Shoe Blog 
I have trouble with Haglunds on my right foot. Neither street shoes nor running shoes bother it. Stiffer hiking and mountaineering boots did. I finally made a “donut” pad of neoprene that provides a cut out for the bump. I tape to my heel and it has solved much of the discomfort that I experienced while hiking.