What does it mean when the market is up or down today?

When people say ‘the market is up or down’, they are usually referring to a major index such as the S&P 500 or Dow Jones Industrial Average. A rise in an index means that its calculated value has increased, while a fall means that its calculated value has decreased. The contribution of individual constituents depends on the index’s weighting methodology. These daily moves are driven by economic data, corporate earnings, geopolitical events, and investor sentiment.