masc. is not a word you say out loud as its own vocabulary item. It is the written abbreviation of masculine. You meet it in dictionaries and grammar notes, especially for languages that give nouns a gender: a French or German noun marked masc. is a masculine noun, which decides which little words sit next to it (like le in French). English nouns do not work that way, so in an English class the label is usually pointing at another language, or at the English adjective masculine itself — “male,” or “having the qualities people have long linked with men.” On some clothing labels masc. is a short way of saying the cut is meant to look masculine. In newer, informal English, especially around fashion and queer talk, people also write masc without the dot as a short, everyday word for a masculine style; that is a later, looser use, and it is not what a learner’s-dictionary abbreviation mark is doing. The full stop (period) is the hint: this is a shortened written label, like adj. or n., not a new stem you add -ing to.