A classic stamp is a postage stamp

Postage stamp

A postage stamp is a small piece of paper that is purchased and displayed on an item of mail as evidence of payment of postage. Typically, stamps are made from special paper, with a national designation and denomination on the face, and a gum adhesive on the reverse side...

 of a type considered distinctive by philatelists

Philately

Philately is the study of stamps and postal history and other related items. Philately involves more than just stamp collecting, which does not necessarily involve the study of stamps. It is possible to be a philatelist without owning any stamps...

, typically applied to stamps printed in the early period of stamp production, e.g., before about 1870. However, as L. N. Williams puts it, "the term has never been satisfactorily defined". Definitions have included stamps issued before 1900, although not all stamps issued before 1900 are considered "classic", while some stamps issued in the first few years after 1900 are considered "classic." Williams suggests that the classic period extends from 1840 to 1875, and James A. Mackay, in his World of Classic Stamps, New York (1972) applied the term to stamps produced from 1840 to 1870.

To some extent it conveys collectors' prejudices for or against particular countries or specialties. For instance, the Canadian stamps of the 1930s are highly regarded for their design and production quality, and are routinely called "classics"; but the term is much less likely to be used of the US stamps of the same period, and very few would characterize the poorly-printed Mexican stamps of the 1930s as "classic", even though Mexico's first stamps, the Hidalgo issue, are equally poor but always considered classics.