em / m are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
em: (noun) a quad with a square body. (noun) a linear unit (1/6 inch) used in printing.
m: (noun) the 13th letter of the Roman alphabet.
em: EH·m
m: EH·m
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)