
A pattern 1 cent 1850, USA.
What are patterns:
Pattern coins are test coins minted for example to test what the coin would like. Pattern coins are often VERY valuable. There are many different kinds of pattern coins.
Pattern coins:
Pattern: Usually a coin minted for testing or a not approved design-coin.

Finland 2 Penniä 1866 Pattern coin.
Essai: Alternative term for Pattern, usually on French and French-speaking countries.

France 2 decimes 1799 essai.
Trial strike: Often a test coin, or a die trial.

Soviet Union 20 Kopeks 1953 trial strike.
Novodel: Russian copy of a pattern coin, made before 1917.

Russian Empire 1 Rouble 1810 Pattern (novodel)
Piedfort: Usually a pattern coin that is about half thicker than a normal coin.

France 1946 piedfort.
Other kinds of pattern coins exist, too.
In stamps and banknotes
Usually in banknotes and stamps, patterns are much rarer.
Specimen banknote: A banknote used in recognizing a banknote, often given to banks.

"Trial" banknote/stamp: Some banknotes either drawn or produced for testing etc. exist. These are very rare.
Specimen stamp: A stamp sent to postmasters so that they can identify valid stamps. (AKA: Muestra, Monster, Muster, Образец)

Set of specimen stamps, Finland 1889.
Do you have/have had patterns?
I have a 10 MK 1889 specimen stamp. I am planning on buying a 1866 2pen and maybe patterns/pattern that cost under 300€ in the future (about 5-10years).
Warning: Due to the amount of people here, I want to ensure the safety. Be careful, I have heard about 1 person who was robbed due to a numismatics forum.