The term M and 'N' Sounds refers to the two categories of nasal consonants in the English language. The first category, M sounds, includes bilabial, labiodental, and alveolar nasal consonants, which are produced by blocking the airway with the lips, teeth, and tongue, respectively. The second category, 'N' sounds, includes velar and uvular nasal consonants, which are produced by blocking the airway with the back of the tongue and the uvula, respectively. The crossword solution NASALS is an acronym for these two categories of nasal consonants.