Noun: an alphabetical list that shows where to find information in a book, or a number that measures change in something like prices or performance. Verb: to arrange or record information in an ordered list.
From Latin 'index' meaning 'pointer, sign, list', from 'indicare' (to point out). It originally referred to a finger or anything that pointed to information.
An index is a pointer—sometimes literally (your index finger), sometimes on paper (a book index), sometimes in data (a price index). All of them exist to quickly point you to something bigger and more complex.
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