The motif itself developed in Persia and India as the boteh — most likely derived from a bent seed pod or cypress tree. The Western name "paisley" doesn't come from that origin at all; it's named after Paisley, a Scottish mill town that mass-produced Jacquard-woven imitations of Kashmir shawls in the 19th century — the copy's hometown eclipsed the original's name.
Structurally it's a teardrop outline with a round body and a slender curling tail, often filled with smaller floral or leaf motifs inside. The traditional tiling alternates each teardrop's rotation by 180° so neighbouring shapes interlock rather than repeat identically.
1960s hippie and psychedelic culture rediscovered the motif — partly through the Beatles' trips to India — and carried it deep into Western pop culture. In CSS/SVG, a single teardrop path drawn with bezier curves sits inside an SVG <pattern>, alternating its rotation from tile to tile.
When to use
Use for boho/vintage moods and scarf or bandana texture. Scale it down too far and the tail detail smears — keep a generous minimum tile size.