Courtesy of GPT-4:
In linguistics, a mora is a basic timing unit in the phonology of some spoken languages, equal to or shorter than a syllable. For example, a short syllable such as ba consists of one mora (monomoraic), while a long syllable such as baa consists of two (bimoraic). A mora can be formed by different segments depending on the language, such as vowels, consonants, or codas. A mora is used to measure syllable weight, which can affect stress or timing in some languages.
Moras are very important in Japanese, as they are used to measure the length of words and utterances, and to determine the accent and pitch of words. In Japanese, each mora is roughly equal in duration, and a syllable can have one or two moras depending on its structure. For example, the word さくら (sakura) has three moras: sa-ku-ra, while the word せんせい (sensei) has four moras: se-n-se-i. Moras are also used in Japanese poetry, such as haiku and waka, where each line has a fixed number of moras.
In Japanese, each word has a relative pitch pattern that depends on which mora has a high or low pitch. The pitch can change the meaning of words that have the same sounds but different accents. For example, the word はし (hashi) can mean "bridge", "chopsticks", or "edge" depending on the pitch accent. The pitch can also drop after an accented mora, creating a contrast between high and low pitches. The pitch accent of Japanese is not fixed for all dialects, and some regions have different patterns or no accent at all.