noun
fashionable pattern; trendy design
Refers to a pattern or design that is currently in fashion, often used for clothing, textiles, or accessories.
今年の流行の柄は花柄です。
This year's fashionable pattern is floral prints.
彼女はいつも流行の柄のスカートをはいている。
She always wears skirts with trendy patterns.
柄 means 'pattern' or 'design' in general, without the implication of being fashionable.
Compound of 流行 (りゅうこう, 'fashion') + の (possessive particle) + 柄 (がら, 'pattern'). The exact historical derivation is straightforward; the phrase simply means 'pattern of fashion'.