What they are, where to buy them...
Graphic Novels from Panini usually come in one of two forms. The first is a standalone story presented in an illustrated graphic format, the second is a series of comic strips covering a main story arc which have been collected and bound into a book.
If you would like to to know more about the history and background of graphic novels, visit the Wikipedia entry.
Panini books and graphic novels are distributed by Turnaround Publishing. You can order copies directly, or get them from specialist book/comic shops, or from online retailers such as Amazon.