Sources of Contact (aka Lead Sources or Referral Sources) define the original contact point for a customer. These are important for revenue tracking. They allow you to pinpoint the amount of revenue that is generated by each of your advertising or marketing efforts. Examples include:
Sources are managed in the Configuration Section. When a new guest is added to your database a source of contact can be chosen from the existing sources or a new one can be typed in. If manually entered the source will automtically be added to your list of possible sources. Each person's source can be modified by the field on the Person Dialog.
In the Finance section a revenue report can be generated by source of contact. This is important for making decisions about marketing efforts. Go to Finance > Revenue > By Referral Source to display the revenue for a timer period by source of contact.