In poetry, a foot is a certain number of syllables forming part of a line of verse, measured for effect in English as long beats (accented) and short beats (unaccented).
In many other languages criteria such as duration of the syllable (long or short) is the effect measured.
... the age of 18, 3.5% from 18 to 24, 22.3% from 25 to 44, 28.7% from 45 to 64, and 28.1% who are 65 years of age or older. The median age is 50 years. For every 100 ...