Hair loss refers to  refers to a loss of hair from part of the head or body.
I thought only males lost hair, but I'm female and my hair is much thinner than it used to be.
It happens to the head
I think it happens elsewhere, too.  My dad is in his 80s, and he literally has NO hair on his legs anymore!
Oh well, one thing I am sure about is that hair loss can vary from a small area