Federal Reserve Chair Jerome Powell is due to address a gathering of central bankers this Friday at a symposium in Jackson Hole, Wyo. Here's what you need to know: **When is Powell speaking and what is he discussing?** The Fed chair is due to talk at 10 a.m. ET on Friday. The Fed says simply that he will discuss the economic outlook. **Why does Powell's Jackson Hole speech matter?** Any public remarks by the Fed chief are potentially market-moving.