Shear webbing is any solid plate verticle member between the upper and lower spar cap in a wing. It is like the verticle part of an I beam.

Its principle purpose is to keep the upper and lower spar spread apart by a fixed amount. This lets the beam formed by the upper and lower spar remain at its design strength. Without the shear web, under high loading conditions the upper spar may fail in buckling and the lower spar may creep up in to the rest of the structure. If the loads are low enough you don't need them

The Sig Kadet LT 40 wing is a fine example the shear webs stop about 3/4 of the way out to the tips because the bending loads at the wing tips are less.

HTH
Tom