polysomnography (psg), a type of sleep study, is a multi-parametric test used in the study of sleep and as a diagnostic tool in sleep medicine. the test result is called a polysomnogram, also abbreviated psg. the name is derived from greek and latin roots: the greek πολύς ("polus" for "many, much", indicating many channels), the latin "somnus" ("sleep"), and the greek γράφειν ("graphein", "to write").