What is Ash Wednesday and why do people have ash marks on the forehead?

ash wednesday
Ash Wednesday occurs 46 days (40 fasting days, if the six Sundays, which are not days of fast, are excluded) before Easter and can fall as early as February 4 or as late as March 10.

Ashes used are from palm branches from the previous Palm Sunday and churchgoers receive ashes in the form of a cross on their foreheads.

ash wednesday cross on your head