What does it mean?
"You've got a five o'clock shadow."
???
This is the sentence to talk about physical characteristics.

Question

What does it mean?
"You've got a five o'clock shadow."
??? 
This is the sentence to talk about physical characteristics.

Answer

A "5 o'clock shadow is the growth of beard on a man's face between the time he shaves in the morning and 5 o'clock in the afternoon. Some men with lighter hair (like me) don't show it. Others with darker, thicker hair have noticable 5 o'clock shadows.

Answer

Some dark haired men have a '5 o'clock shadow' by lunch time!

Answer

A "5 o'clock shadow is the growth of beard on a man's face between the time he shaves in the morning and 5 o'clock in the afternoon.  Some men with lighter hair (like me) don't show it.  Others with darker, thicker hair have noticable 5 o'clock shadows.
It is called that because it resembles a shadow on the face somewhat.