This is the 7159th most frequent Spanish word.
flaco
Thin; skinny.
The word 'flaco' is used here to describe someone who is physically thin or slim.
Mi amigo es muy flaco y siempre lleva ropa ajustada.
My friend is very skinny and always wears tight clothes.
In this context, 'flaco' is used to describe the thinness of an object, emphasizing its fragility.
Esa cuerda está tan flaca que no soportará el peso.
That rope is so thin that it won't hold the weight.
Here, 'flaco' metaphorically describes someone as being mentally or emotionally weak.