What does "generic vertex attribute" mean in the context of the function "glVertexAttrib4*"?

What does "local parameter" mean in the context of the function "glProgramLocalParameter*"?

What does "environment parameter" mean in the context of the function "glProgramEnvParameter*"?

Also the explanation available of the argument usage is confusing? Can anybody please explain the usage of the above APIs, especially how the "index" argument in each API work.

Thank you