Colloquial and slightly childish or informal term for the buttocks. Often used in casual or affectionate contexts.
The baby's bottom is soft and squishy.
I fell and hit my backside.
Variant spelling with small ぺ; less common.
Compound of 尻 (shiri, 'buttocks') and ぺた (peta), a colloquial suffix possibly from ぺたんこ (petanko, 'flat') or onomatopoeic for slapping, giving a playful or childish tone.