noun
soap bubbles; soapsuds; lather
Refers to the foam or bubbles produced by soap, often when washing hands, face, or dishes.
手を洗うとき、石鹸の泡がたくさん出た。
When I washed my hands, a lot of soap bubbles came out.
石鹸の泡で顔を洗う。
I wash my face with soap lather.
石鹸 means 'soap', while 石鹸の泡 is the lather or bubbles produced by soap.
Compound of 石鹸 (sekken, 'soap') + の (no, possessive particle) + 泡 (awa, 'bubble'). The exact historical derivation is straightforward; the spelling is conventionally associated with the meaning.