hairline
n.the edge where your hair meets your forehead. It can change shape or move higher as you get older.
n.the edge or outline of the growth of hair on the head, especially across the forehead. Often used to describe the progression of male pattern baldness.
“He noticed his hairline was starting to recede.”
“The barber carefully trimmed the edges to create a sharp, clean hairline for the client.”
“Genetic factors largely determine the shape of one's hairline, though environmental stressors and age can cause the follicles to thin over several decades.”
Commonly modified by adjectives like 'receding', 'high', or 'widow's peak'.
“Don't forget your hairline and any partings to protect your scalp.”
From hair + line.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.