Name of shape with constant distance to a line segment [duplicate]

Maybe it is a ciiiiiiiiircle?

Kidding aside, I've never seen a dedicated name for it, but in metric topology one can always define the set of points at distance $R$ from a given set.

I also ran across this question in another forum which appears to be asking the same thing. It is again a lot of "I don't know a specific word for it" but the words that came up were things like "race track", "truncated circle" and "stadium." (Note while some of the posters mention elliptical shapes, the OP there clearly stated he's asking about a circle split in half reconnected with straight sides to make the shape the OP is asking about here.)

Wikipedia also suggests that in common English, the "split circle connected by lines" is often called an oval, and that this name is applied to oval tracks.

Edit: Arthur noted in the comments that if you happen to follow the link to stadium, it suggests that stadium is exactly the word you're looking for. I guess if the line gets longer, you just call it a long stadium.

In my searches for terms, I came across this article on topological skeletons which seems to be a sort of "backwards" version of this problem where you start with a shape and then find points inside that are as "central" as possible.

I got the idea then to try to find answers under the heading of shape analysis, but I also ran out of luck with search terms. It seems like a promising clue, though.

Another name is obround, which can be a noun or adjective.

ob-

(non-productive) Against; facing; a combining prefix found in verbs of Latin origin.

Example from manufacturing: