Stress, strain, pressure, tension are comparable terms when they apply to the action or effect of force exerted within or upon a thing.
Stress and strain are the comprehensive terms of this group and are sometimes used interchangeably.
Although stress is frequently used in technical contexts in the above sense of a force applied to deform a body, it is also used, especially in physics, of the equal and opposite forces with which the body resists being deformed.
Strain in technical contexts and especially in physics usually denotes the deformation of a body as a result of applied force.
Pressure commonly applies to a stress which is characterized by a weighing down upon or a pushing against a surface and which, in fluids, is distributed uniformly in all directions; it is usually measurable per unit area of surface affected.
Tension applies to either of two balancing forces causing or tending to cause elongation of an elastic body or to the stress resulting from the elongation of such a body.