What is tension force in static equilibrium?
Concerning forces, an object/system is said to be in equilibrium when the net force acting upon it is zero (forces are balanced). Static equilibrium describes a situation where the net force is zero and the object is not in motion (as opposed to dynamic equilibrium, in which the object is in motion).
If you had a mass suspended from a rope which was not moving, the tension force in the rope holding the object up would be equal and opposite to the force of gravity pushing the object down. The forces are balanced, and so the net force on the box is zero. Therefore, it does not move, and is in a state of static equilibrium. If the force of gravity were greater than the tension in the rope, the rope would break, and the object would accelerate downwards-no longer in equilibrium-until coming to rest on the ground (back into static equilibrium).