Market efficiency is a term used in economics and finance to describe a market in which prices reflect all available information. In an efficient market, prices are determined by the interactions of buyers and sellers, and all relevant information is quickly and accurately incorporated into prices.
There are different levels of market efficiency, ranging from weak-form efficiency (where prices reflect all past information) to strong-form efficiency (where prices reflect all public and private information).
It is a subject of debate among economists and financial experts whether stock markets are efficient. Some argue that stock markets are relatively efficient, especially in developed countries where there is a high level of transparency and information is readily available. Others believe that stock markets are not always efficient, and that prices can be influenced by a variety of factors, including investor psychology and market manipulation.