This is the 17041st most frequent Russian word.
спина
Back (part of the body).
Here, 'спина' refers to the physical part of the body, the back. It is used to contextualize a physical condition.
У меня заболела спина после долгой работы в огороде.
My back started hurting after working in the garden for a long time.
In this sentence, 'спина' indicates the position or orientation of someone's body, specifically their back turned away.
Он повернулся ко мне спиной, чтобы скрыть свои эмоции.
He turned his back to me to hide his emotions.
Here, 'спина' is metaphorically used to describe the spine of a book, indicating its physical structure in an extended sense.