M-N-O refers to the sequence of letters in the English alphabet, specifically the 13th, 14th, and 15th letters. These letters are often used in various contexts, such as in spelling, phonetics, and categorization. For example, in the context of music, M can represent major, N can denote natural, and O can signify octave. In addition to their alphabetical significance, M-N-O can also represent a range of concepts in different fields. In mathematics, these letters might be used to label points or variables. In education, they can be part of learning tools, such as flashcards, to help students memorize the alphabet and improve literacy skills.