A shader profile describe the target when compiling a shader. It is a short string with the type of shader first and then the shader model version number. Ex vs_5_1 for shader model 5.1 vertex shader.
There are five possible shaders that can be used in HLSL. The most common is the Vertex and the Pixel shader.
Vertex Shader - vs_5_1
Performs per-vertex processing such as transformation and skinning.
Hull Shader - hs_5_1
Domain Shader - ds_5_1
Geometry Shader - gs_5_1
Pixel Shader - ps_5_1
Performs per-pixel processing such as lighting and texturing.
Root signature blob - rootsig_1_0
Not a shader stage but a valid compile target. Can then be used when compiling other shaders.
The shader model is the version numbers for the High Level Shading Language.