"Imperfection is beauty, madness is genius and it's better to be absolutely ridiculous than absolutely boring."
This stamp of Ben Franklin from the United States Postal Service was issued in 1851 with a face value of one cent. The stamp was used to pre-pay certain types of mail like circulars or what is known today as junk mails.
The 1-cent Ben Franklin stamp varies considerably in its design. The imperfection in the design is due to the technical difficulties in making the plates causing the stamps to appear incomplete, mostly at the top and bottom borders. To further differentiate the varying degrees of incompleteness, the stamps have been identified by its type or subtypes. Needless to say, the various research that went to study these types of flaws has shaped how these stamps are identified and valued by the stamp collecting community.
If you're interested in learning more about Ben Franklin's many types of imperfections, the Philatelic Foundation has written an excellent article about it which you can read here.