noun
frame of a shoji; shoji lattice
Refers to the wooden lattice framework of a shoji, the paper-covered sliding door used in traditional Japanese architecture.
古い家の障子の桟が外れかかっていた。
The frame of the shoji in the old house was coming loose.
桟 alone can mean a crosspiece or bar in various contexts, but 障子の桟 is the specific term for the shoji frame.
Compound of 障子 (shōji, 'paper sliding door') + の (possessive particle) + 桟 (san, 'crosspiece, frame'). The reading さん for 桟 is the standard on'yomi.