Meaning
A pair of briefs, the snug kind that can be underwear or swim trunks, usually shown in a solid colour. It is a practical everyday item rather than a fashion statement.
It is used for laundry, packing lists, swimming and cheeky jokes: “Packed everything except 🩲, classic me.” Because it can mean underwear or swimwear, context decides; swimmers and divers often use it for their trunks.