For the benefit of stamp collectors, Gustamps have been publishing info about some philatelic terms. Here is today's stamp term explained by Gustamps.
SURCHARGES
These are overprints on stamps which change the original denomination on the stamp. Gustamps explain that surcharges can be printed in numerals or words. For example, Gustamps explain, a two cent stamp surcharged half cent reduces the postal value of the stamp to half a cent. Gustamps point out that although it decreases the postal value, it could increase the philatelic value to a stamp collector.