RF stands for "Reichsfürst", i.e., the head of the house in question had an individual seat and voice in the Imperial Diet; there were ten of these (Fulda, Kempten, Ellwangen, Murbach-Lüders, Berchtesgaden, Weissenburg, Prüm, Stablo-Malmedy, Corvey and St. Gall).
ˌɑːɹɹˈɛf stˈændz fɔːɹ "ɹˈaɪxsfuːəst", ˈaɪ.ˈiː., ðə hˈɛd ʌvðə hˈaʊs ɪn kwˈɛstʃən hæd ɐn ˌɪndᵻvˈɪdʒuːəl sˈiːt ænd vˈɔɪs ɪnðɪ ɪmpˈɪɹiəl dˈaɪət; ðɛɹwˌɜː tˈɛn ʌv ðiːz fˈʊldə, kˈɛmpʔn̩, ˈɛlwændʒən, mˈɜːbɑːxlˈuːdɚz, bˈɜːtʃtɪsɡˌædən, wˈaɪsənbˌɜːɡ, pɹˈuːm, stˈæbloʊmˈælmədi, kˈɔːɹveɪ ænd sənt. ɡˈɔːl.