An object in equilibrium is at rest. It is not moving (or "translating") and it is not rotating.
There are two conditions of equilibrium.
That a body is not moving (or "translating") means the sum of the forces is zero,
F = 0
That a body is not rotating means the sum of the torques is zero,
We can also write this Second Condition of Equilibrium as
A torque is a "rotational force" or the rotational equivalent of a force,
torque = moment arm x force
The behavior of a material as it is deformed is described by a modulus,
Deformation of Solids Homework Return ToC, Static Equilibrium (c) Doug Davis, 2001; all rights reserved