Why is one side of the moon caled the dark side of the moon?

The term "dark side of the moon" is a misnomer; it refers to the side of the Moon that is always facing away from Earth due to synchronous rotation. This side is not perpetually dark, as it receives sunlight just like the side that faces Earth. The phrase gained popularity due to the mystery and lack of direct observation until space missions revealed its features. Today, it's often used metaphorically to describe hidden or unexplored aspects of something.