An equality constraint appears as an EQ symbol near the dimension line when you select a multi-segmented dimension. If you select one of the references for the dimension line (such as a wall), the EQ symbol appears with a dashed blue line at the middle of the references.
The EQ symbol represents an equality constraint element applied to the references for this dimension. The references, which are walls in the graphic, remain at equal distances from one another while this constraint is active. If you select one of the walls and move it, all walls move together at a fixed distance.