A First Edition is the first commercial print run of the book. These are normally the most collectable versions of the book. These books are hard bound editions.
Pictured right: inside cover from V S Naipaul A Flag on the Island - First Published 1967
Normally these books feature the words First Published, First Printing or even First Edition.
If the book is successful their maybe subsequent editions or printings - second printing, third printing etc.
Pictured right: inside covers from Tom Stoppard Travesties (1975) 1st Edition -
First Published in 1975
A First Edition is the first commercial print run of the book. These are normally the most collectable versions of the book. These books are hard bound editions. 
Pictured right: inside covers from Tom Stoppard Travesties (1975) 1st Edition -