A bird is flying overhead.
There was a sign warning of overhead hazards.
A sky full of stars spread out overhead at the campsite.
A fighter jet flew low overhead.
At construction sites, things can fall from overhead.
The ceiling is low, so please watch your head overhead.
頭上 points to the area above one's head, whereas 足元 points to the area at one's feet, the opposite end of the body.
頭 is the body part 'head' itself, while 頭上 refers to the space directly above that head, not the head itself.
Compound of 頭 (head) and 上 (above). The reading ずじょう is a standard on'yomi combination.