What exactly is "авторская песня"?

What does "авторская песня" exactly mean in Russian music? Is it a folk song? Or something similar to "русский шансон" or "блядская песня"? Or similar to bard songs like Vysotsky, Okudzava or Bashlachev's music? Or something bigger than those categories?

Also, are only "bard songs with acoustic guitar(no electric instruments), poem-like lyrics with traditional Russian rhyming" recognized as авторская песня?