Selects a point at the middle of a line
The Middle snap places the point in the middle of the selected line or arc.
If nothing is selected, the Middle snap finds the closest line or arc and uses the middle of that. If there are no entities in the drawing, LAYOUT uses the point where you clicked.
Using the Middle snap can divide an entity in two at the midpoint, depending on the setting in Options. After using Middle on a line, for example, the line would be divided into two lines of equal length.