The season when leaves fall from trees; autumn.

Season between summer and winter. Astronomically it is the period from the autumnal equinox to the winter solstice in the Northern Hemisphere.

the season when the leaves fall from the trees; "in the fall of 1973"

Autumn – the season between summer and winter is called Fall throughout North America.

Indiana University divides the school year into two semesters—fall and spring. The fall semester generally begins in late August or early September and ends in mid-December. Fall also refers to one of the four seasons (divisions of the year) experienced in Indiana. Fall, also called autumn, is comprised of the transition months of September, October, and November when the weather begins to cool and winter approaches.

autumn fanny (buttocks) bum [colloq.

Don't capitalize; for example, "fall semester," "fall 2001."