An economic calendar is a tool used by investors to track events that have market-market changing potential, economic indicators and monetary policy decisions are a good example.
Market-moving events which are typically announced or released in a report, have a very high probability of impacting the financial markets, thus an instrument that allows you to track all of the events on one dashboard is quite effective.
An economic calendar is usually displayed as a chart showcasing time periods such as days, weeks and months per a specific year. Each day lists several market-moving events in chronological order, allowing investors time to research and anticipate the specific release(s) of interest to them, with several online sites allowing push notifications, email reminders and and option to add such events as a notes to your portfolio.
Since knowledgeable speculations are an asset in the financial markets - most economic calendars suggest forecasts and later compare to actual results of the announcements - allowing investors a glimpse of the economic calendar's foresight accuracy.