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You mean a Squircle®

Technically, a quintic superellipse, in modern times.

That's of course not what the patent was about.

You can also patent the shape of a bottle. https://patents.google.com/patent/USD48160S/en (yes, its an old one).

These fall into the classification of design patent which covers ornamental non-functional elements of a particular item. https://en.wikipedia.org/wiki/Design_patent

Design patents also cover typefaces. https://en.wikipedia.org/wiki/Intellectual_property_protecti... -- note that typefaces cannot be copyrighted in the United States

Design patents differ from a utility patent which covers how something works.

Design patents are a form of trademark with a silly name, not real patents.

Design patents expire, unlike trademarks.