This is the 11386th most frequent French word.
reins
Kidneys.
The word 'reins' is used to refer to the lower back or kidney region in this context.
Elle a des douleurs aux reins après avoir soulevé des objets lourds.
She has pain in her lower back after lifting heavy objects.
The word 'reins' refers to the straps used to control a horse in this sentence.
Le chevalier prit les reins du cheval pour mieux le diriger.
The knight took the reins of the horse to direct it better.
Here, 'reins' metaphorically means taking control or leadership of a situation.