Title used before an adult woman's name or surname, especially when it is not desired or possible to indicate her marital status with Miss or Mrs.
There is some difference of opinion regarding the use of apostrophes in the pluralization of references to letters as symbols. New Fowler's Modern English Usage
How often have the words Ms and There is some difference of opinion regarding the use of apostrophes in the pluralization of references to letters as symbols. New Fowler's Modern English Usage occurred in a corpus of books? (source: Google Ngram Viewer )