noun
one step above; a cut above; one better
Idiomatic noun/adjectival phrase meaning someone or something is superior or a notch above another. Often used in comparisons with より or の.
彼の料理の腕はプロより一枚上だ。
His cooking skills are a cut above the pros'.
この新製品は従来品より一枚上の性能を持つ。
This new product has performance that is a notch above the conventional one.
From 一枚 (one sheet/one item) + 上 (above). The exact origin is uncertain, but it likely comes from the idea of being one rank or layer above in a stack or hierarchy.