Static equilibrium is a form of equilibrium that occurs when an object is at rest. "Static" refers to the object being motionless while "equilibrium" refers to the object either having no net forces acting upon it or having all of its net forces balanced.
The state of an object relative to equilibrium is determined by the net forces acting upon it. Each force that acts on an object must be determined and quantified. Then, the vector forces can be added together. If they equal zero, then the object is in equilibrium. If the forces are zero and the object is at rest, then the object is in static equilibrium.