What is the difference between vocalese, scatting, and ranting?

As I say, vocalese was invented by Eddie Jefferson, and is the writing and performing of a lyric which has been tailored to fit the lines of an instrumental solo from someone else's record. Eddie fell in love with Charlie Parker records. He listened to them so much that he memorized the solos and started singing them. Words and stories naturally started to occur to him when he heard the solos in his head, and he wrote them down & began a new career for himself performing them. His most famous lyric, written in 1946 to James Moody's solo on “I'm In The Mood For Love”, was made famous by a King Pleasure (Clarence Beeks) hit recording of the lick in 1952.
The magnificent vocal trio Lambert, Hendricks and Ross brought the performance of vocalese to its zenith in the late 50's and early 60's with their interpretations of Count Basie, Duke Ellington and Wardell Gray charts. Jon Hendricks is the acknowledged master of the writer's art, and has continued supplying the world with fantastic and astonishing creations to this day. Dave Lambert, who died some years ago, did most of the musical arranging for the original group (for three voices and rhythm section). Annie Ross, the third member of the trio, though not a full-time lyricist, wrote some of the most famous lyrics, including “Twisted” and “Jackie”.

Of course, the most famous and accomplished group to have followed LHR has been The Manhattan Transfer. (From my own recordings, check out “Those Clouds Are Heavy, You Dig?” from Close Your Eyes or “Night Dreamer” from Live in Chicago.)

Scatting, properly defined, is the art of composing a solo in the here-and-now, using whatever nonsense syllables the singer requires to do so. Ella Fitzgerald was famous for this, and has inspired many of today's aspiring and professional Jazz singers. The greatest living example of a Jazz-based improviser in this vein is Bobby McFerrin, who is the ultimate example of singer as musician. He is omnicompetent. (For an example of scatting from my own recordings, I suggest “My Love, Effendi” from This Time It's Love.)

“Ranting” is an informal term a friend of mine came up with for improvised melodies coupled with improvised lyrics. Sometimes there is no melody – just an improvised story or “open thought process”. (Good examples of these on my own records are the open, middle section of “The Beauty of All Things” and the spoken section “The Messenger” from The Messenger.)