A forecast is a 'window' into what revenue is coming in to the business. It can show the potential sales volume for the entire business, volume by sales manager / team, etc. In the forecast feature in a CRM, you can assign sales quotas to sales managers and compare their forecasts and actual sales with the quota. Forecast information comes from the opporunities entered by the sales manager. This is why it is very important to maintain the CRM with accurate sales information.