This is a old-fashioned taxonomic word used to describe different populations of the same species that may be slightly different (such as the black peppered moth and the white peppered moth - both are from the same species, but have different colouration - or the wide range of domestic dogs that humans have bred). Varieties can still breed with each other and produce fertile offspring, but they are at the start of the process that might one day (in millions of years) produce two new species.
Different forms within a Species that are quite different, yet fall under the same general category as species.
This term normally refers to different printings of the same stamp, e.g. changes in paper, watermark, gum, perforation, phosphors etc.