A mora is a unit of poetic timing used in quantitative meter. In classical prosody, a short syllable counts as one mora, and a long syllable counts as two. Poets and scholars use morae to describe how patterns of duration, rather than stress alone, shape a line's meter.
Example
Short = 1 mora
Long = 2 morae
A line built on 2 + 2 + 1 + 2 would move like:
daa | daa | da | daa