Say you are standing in your backyard.
If you look straight up over your head, that is your zenith.
It is the intersection of the imaginary north, south, east, and west lines rising from the horizon of your field of vision.
In general terms, the zenith is the direction pointing directly “above” a particular location, and is important in in astronomy and related sciences, including meteorology.
The word zenith comes from the Arabic expression سمت الرأس which means “direction of the head”, or “path above the head”.
The Middle English word “senith” became “zenith”, and first appeared around the 17th century.