This means that the person speaking will pay the whole amount, used typically when something purchased is shared between two or more people - such as a resturant meal.
Dinner was $40 - here is my $20.
No, keep your money, it's on me.
a book, usually some type of hip or classic piece of literature, that you bought and read 14 pages of it and never finished, yet you left in casual display in your living area so people think you're well read.
-1"Yo have you seen the movie Fear and Loathing?"
-2"nah, but i read the book."
-1 "I heard the book is good. Did you like it."
2- " Well I never actually read it. it's on my bookshelf though.