Definitive stamp

[3] Commonly, a definitive issue or series includes stamps in a range of denominations sufficient to cover current postal rates.

An "issue" generally means a set that is put on sale all at the same time, while a "series" is spread out over several years, but the terms are not precise.

The definitives of poorer countries will often be very plain and cheaply printed, unlike the large and decorative commemoratives, which are almost pure profit if bought by foreign collectors and never used for postage.

Since definitive series are issued over a period of time and are reprinted to meet postal demand, they often contain more variation than is typically found in stamps that have a single print run.

One notable example of this variation is the Machin stamps of the UK, where philatelists have identified over 1,000 varieties of the same basic design.