Originally ARM stood for Acorn RISC Machine, and this article explains the history of Acorn.

Originally ARM stood for Acorn RISC Machine, and this article explains the history of Acorn. According to this Are Technica article, the origin of the ARM chips involves a BBC TV show and a Slot Machine software company called Acorn. https://arstechnica.com/features/2020/12/how-an-obscure-british-pc-maker-invented-arm-and-changed-the-world/