New Definitive "Birds" Overprint by Gibraltar Post
An overprint is an additional layer of text or graphics added to the face of a postage stamp, banknote or postal stationery after printed. Post offices most often use overprints for internal administrative purposes such as accounting but these have also been employed in the past for public mail.
Gibraltar's last overprinted stamp was released in 1991 when the 1987 Definitive Guns with the original value of £3 was overprinted with a £1.05 value. Due to the fact that new postal rates are being introduced in Gibraltar with the latest Christmas stamps, the Post Office required two additional values, a 14p and 28p.