A single petal of a flower. Often written in hiragana (はなびら); the kanji 花弁 is also used.
公園に花びらが散っている。
Petals are scattered in the park.
風で桜の花びらが舞っていた。
Cherry blossom petals were dancing in the wind.
花びらを一枚ずつ慎重に集めた。
I carefully collected the petals one by one.