In general, artists like working with a linear roughness value between 0 and 1 (similarly for all other material parameters), since this is easier to work with and to understand compared to directly using the parameters of certain BRDF components as presented in the literature. Disney for instance always uses linear material parameters for their Disney BRDF in the range [0,1] from the perspective of the artists (see their course notes on page 18). Working with linear values in the range [0,1] also simplifies storing and loading these values in RGB or sRGB textures.
The actual roughness used in the BRDF equations is non-linear. So one needs to map linear to non-linear roughness in some computationally cheap way that pleases the artists. The most important thing is to be consistent across your renderer and to explicitly specify when a roughness parameter is linear or non-linear.
It is worth reading Moving Frostbite to Physically Based Rendering 3.0. These course notes explicitly use the terminology linear roughness and (non-linear) roughness, both in the text and code samples. Furthermore, it is also worth reading The Specular BRDF Reference which defines various BRDF components for the Cook-Torrance BRDF using the same non-linear roughness parameter $\alpha$ (defined as the square of the linear roughness $roughness$).
