The full name of this property is "modulus of elasticity in shear". However, the term "modulus of elasticity" by itself is typically used to refer to tensile loading (and compressive for metals, where the two track each other closely). The shear modulus is the same slope of the elastic region of the stress-strain curve, but under shear loading.
The term "modulus of rigidity" is a synonym (not to be confused with "modulus of rupture", which is a synonym for flexural strength).
In some cases, a material's shear modulus can be estimated from the tensile modulus and Poisson's ratio.