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The stremma (pl. stremmata; Greek: στρέμμα, strémma) is a Greek unit of land area now equal to precisely 1,000 square meters. It is also known as the royal stremma to distinguish it from earlier forms of the unit.
A barn (symbol: b) is a unit of area equal to 10−28 m2 (100 fm2). Originally used in nuclear physics for expressing the cross sectional area of nuclei and nuclear reactions, today it is also used in all fields of high-energy physics to express the cross sections of any scattering process, and is best understood as a measure of the probability of interaction between small particles.