wave on the water's surface
Archaic term for a wave visible on the surface of water. In modern Japanese, 波 (なみ) or 水面の波 would be used instead.
In old waka poetry, 上波 can refer to waves on the water's surface.
Compound of 上 (うわ, 'upper, surface') and 波 (なみ, 'wave'). The exact historical derivation is uncertain, but the spelling is conventionally associated with the meaning 'surface wave'.