Why bubble sort is called bubble sort?

It's called bubble sort because in one iteration of the algorithm smallest/largest element will result at its final place at end/beginning of an array.

So in some sense movement of an element in an array during one iteration of bubble sort algorithm is similar to the movement of an air bubble that raises up in the water

Why is it called bubble sort?

The bubble sort gets its name because elements tend to move up into the correct order like bubbles rising to the surface.