In physics, elasticity is the ability of a body to resist a distorting influence and to return to its original size and shape when that influence or force is removed. Solid objects will deform when adequate forces are applied to them. If the material is elastic, the object will return to its initial shape and size when these forces are removed. (extracted from Wikipedia)

In breadmaking, elasticity refers to the strength of the dough, completely related to the gluten development in it, producing an elastic and pliable dough, able to grow and expand, without tearing apart or deflating while baking or fermenting.