Regarding the title of the 'Invincible' album, here is why that word was chosen (as shown by the promo slogan that unveiled the album title):
"First it was Off the Wall, then Thriller. He's Bad and Dangerous. He's made music HIStory over and over again. He is in a word, INVINCIBLE. That's right folks. INVINCIBLE is the title of the King of Pop's new CD" (MJNI)
Michael Jackson also wanted to give a playful meaning to that album title, just like his 'Dangerous' album:
Before listening to the 'Dangerous' song you think that he is Dangerous, but after listening to it you realize that actually the girl is Dangerous.
In the same way, before listening to the 'Invincible' song you think that he is Invincible, but after listening to it you realize that actually the girl is Invincible.