In an alphabet, each symbol stands for one sound, either a vowel or a consonant. In a syllabary, each symbol stands for a whole syllable, usually a consonant-vowel pair. So, in Japanese, there is no separate letter for "M." There are 5 symbols, ma, mi, mu, me, mo. (in Hiragana, まみむめも。) Korean also uses a syllabary,
Hangul, but the Korean syllabary was designed to be remarkably consistent and logical, based on phonetic sub-symbols known as Jamo.