middle pine tree on a Noh stage
Refers to the second of three stylized pine trees placed along the bridgeway (hashigakari) of a Noh stage. Domain-specific term used in Noh theater.
On the Noh stage's bridgeway, the first pine, second pine, and third pine are arranged.
Compound of 二 (ni, 'second') + の (no, possessive particle) + 松 (matsu, 'pine tree'). The term is specific to Noh theater staging conventions.