What does the tag SBAR mean in Stanford’s parse-tree representation?

Question

When the Online Stanford Parser tool is fed this original sentence:

After she ate the cake, Emma visited Tony in his room.

It produces the following parse-tree representation as its output:

(ROOT
  (S
    (SBAR (IN After)
      (S
        (NP (PRP she))
        (VP (VBD ate)
          (NP (DT the) (NN cake)))))
    (, ,)
    (NP (NNP Emma))
    (VP (VBD visited)
      (NP
        (NP (NNP Tony))
        (PP (IN in)
          (NP (PRP$ his) (NN room)))))
    (. .)))

My questions are:

1. What does the SBAR tag mean?
2. Why are there two different S tags?
3. What is the correct NLP parse-tree representation of this sentence?

Answer 1

SBAR stands for Subordinate Clause (see here). In your case the subordinate clause starts with the subordinate conjunction After