Economists are scientists who study economics. They study market conditions by analyzing economic data that is released daily, and try to explain what is affecting the economy. They predict how current market conditions will alter future government fiscal and monetary policy.They based their predictions on theory and how the market should act.
Economists are more concerned with the longer term outlook of the economy, because there are normally delays when the government makes changes in policy.
Take note, while some economists do trade, not all are traders.