Market in which prices correctly reflect all relevant information. Bloomberg Financial Dictionary
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A market in which security prices reflect information instantaneously. Exchange Handbook Glossary
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efficient market UK US noun [S] ECONOMICS
► a market where all the important information is available to everybody involved at the same time, and prices change immediately according to this information: »
In an efficient market, prices reflect all available information, and so past prices can tell you nothing useful about whether future prices will go up or down.
Financial and business terms. 2012.