Semantics

waist
Ћн тќхо ћбнял стрћйный её стђн и тќхо привлёк её к своемџ сљрдцу. [А. Пџшкин, Дубрћвский] He slowly encircled her shapely waist, and slowly drew her to his breast. [A. Pushkin, "Dubrovsky"]
torso
[Ћн] мгновљнно охватќл глазђми её облечённый в бљлую кћфту и тёмную єбку стрћйный стђн с гќбкой и сќльной тђлией. [А. Фадљев, Молодђя гвђрдия] In an instant his eyes captured her well-built, white-sweatered and dark-skirted torso with its lithe, strong waist. [A. Fadeev, The Young Guard]
body
... онђ повернџлась на стџле, легкћ и естљственно изогнџла длќнный стђн, достђла с буфљта сзђди пљпельницу... [В. Набћков, Дђр] ... she turned in her chair, easily and naturally twisted her long body, obtained an ashtray from the sideboard behind her... [V. Nabokov, The Gift]
This entry is concerned with the use of the word стђн to refer to the part of a human torso from the lower ribs to the upper abdomen as an element of the figure or to the upper portion of the torso, e.g. длќнный стђн "a long waist." This word is used in poetic style to describe the shape of someone's body and also certain gestures and movements involving someone's waist. It does not refer to animals.