Commonly stands for 'National Cash Register' company, or in mathematics, 'n choose r' (combinations formula). Can also refer to no carbon required paper.
As an acronym, emerged in the early 20th century with the National Cash Register Company founded in 1884. The mathematical usage developed independently from notation in combinatorics theory.
NCR revolutionized retail by creating the first mechanical cash registers, but their real innovation was the paper receipt - they literally invented the concept of transaction documentation that we now take for granted in every purchase.
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