The mora is a unit of sound. It is between a segment and a syllable. A syllable with one mora is monomoraic. If it has two moras, it is bimoraic.
A short syllable has one mora and a long syllable has two. The onset of the syllable never has a mora. The nucleus has one mora if the vowel is short and two if the vowel is long or is a diphthong. In many languages, the syllable coda is also a mora. For example, the English word "cat" is bimoraic.
Japanese speakers are very much aware of the mora. In fact, the Japanese haiku poem consists of 17 moras divided into verses of 5, 7 and 5. "Tokyo" has two syllables but four moras because the two vowels are long- to-o-kyo-o. "Osaka" has three syllables but also four moras- o-o-sa-ka. "Sapporo" also has four moras- sa-p-po-ro.
Hungarian is a language which can have short and long consonants in the syllable coda. For example, "megy" is the verb "goes" and "meggy" is "sour cherry". The word "megy" has two moras and "meggy" has three.
Moras are closely connected to duration and syllable weight. If a syllable has no coda, it is a light syllable. If it has a coda, it is a heavy syllable. However, a syllable that ends in a diphthong can be classified as light but has two moras as in "day" and "my".
The mora is a unit of sound which is often associated with syllables. It is possible for a syllable to have more than one mora. Japanese is one language which is famous for its use of moras. They are the units used for writing haiku.