An altered book is an existing book that has been changed or altered using glue, paint, collage, rubber stamps, and scissors, tearing, or adding to. "It is an expression of one's self, a piece of art, an experiment or a conversation piece."
In short, an existing book that has been changed or altered with glue, paint, collage, rubberstamps etc. There are infinite numbers of things you can do with a book form to turn it into something else &mdash everything from making an embellished or decorated piece of book art to using the book's form in a new way for a completely different purpose of function. (For example, ‘gutting' the book and turning the empty covers into either another book or, say, a purse or frame, or something you wouldn't normally associate with a book form.)