leaf; blade (of grass); (pine) needle
「葉」 has another reading with different meanings.
counter for leaves, pieces of paper, etc.
秋になると葉が落ちます。
Leaves fall when it becomes autumn.
秋になると葉が落ち始める。
Leaves are falling.
秋になると、木の葉が黄色くなります。
When autumn comes, the tree leaves turn yellow.