In structural engineering, a shear wall is defined as a structural system composed of braced panels (or shear panels) to counter the effects of lateral load acting on a structure. Wind and seismic loads are the most common loads that shear walls are designed to carry.
Shear walls are also defined as vertical elements of the horizontal force resisting system. Shear walls have four parts: Framing members, Sheathing, Nails and  Hold-downs. The length of a shear wall is determined by the location of the hold-downs. When the sheathing is properly fastened to the stud wall framing, the shear wall can resist forces directed along the length of the wall. When designed and constructed properly, shear walls will have the strength and stiffness to resist the horizontal forces.
Source.

...