There is a section called "'MUMPS' vs. 'M' naming debate" in the wikipedia article. https://en.wikipedia.org/wiki/MUMPS https://en.wikipedia.org/wiki/MUMPS "So

There is a section called "'MUMPS' vs. 'M' naming debate" in the wikipedia article. https://en.wikipedia.org/wiki/MUMPS https://en.wikipedia.org/wiki/MUMPS "Some of the contention arose in response to strong M advocacy on the part of one commercial interest, InterSystems, whose chief executive disliked the name MUMPS and felt that it represented a serious marketing obstacle. Thus, favoring M to some extent became identified as alignment with InterSystems."