The efficient-market hypothesis is one of the most widely discussed topics in finance and economics. However, there are several synonyms which refer to the same concept such as the random walk theory, the efficient capital market theory, and the informationally efficient market. All of these theories suggest that the stock prices represent all publicly available information and move in a random manner. Consequently, it is almost impossible for investors to consistently outperform the market by using any publicly available information. While these concepts are similar, each has its own nuances, and investors and researchers continue to explore new ideas that build on or challenge their assumptions.