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A mora (plural morae or moras; often symbolized μ) is a theoretical or perceptual smallest unit of timing, equal to or shorter than a syllable, that exists in some spoken languages in which phonetic length (such as vowel length) matters significantly. For example, in the Japanese language, the name of the city Ōsaka (おおさか) consists of three syllables (O-sa-ka) but four morae (O-o-sa-ka), since the first syllable, Ō, is pronounced with a long vowel (the others being short). Thus, a short vowel contains one mora and is called monomoraic, while a long vowel contains two and is called bimoraic. Extra-long syllables with three morae (trimoraic) are relatively rare. Such metrics based on syllables are also referred to as syllable weight. In Japanese, certain consonants also stand on their own as individual morae and thus are monomoraic.
The term comes from the Latin word for 'linger, delay', which was also used to translate the Greek word χρόνος : chrónos ('time') in its metrical sense.