A philatelist is someone who collects and studies postage stamps. Philatelists research, study, and exhibit the production, use, and collection of stamps. Examples of areas of study include: How the postage stamp was designed; the printing process used (such as line-engraved, lithography, gravure); the make-up of the stamp, such as the paper type, gum, and perforations; the varieties of a stamp, such as shade differences and ink markings; errors on stamps, whether spelling mistakes or printing errors: the study of fake or forged stamps and the forgers who created them.

Source: All About Stamps