Tanget Space Normals

I plan to use the tangent space normals baked in blender in one of my projects.
As i understood to use normals in tangent space you need a tangent a bitangent and a normal. My question is which of these component does blender bake in the tangent space normal map

baking a “normal map” makes ain image, which only contains normals, other information is gotten other ways. The only other normals are exported with a mesh file,