Imagine a huge social event (Like a Church BBQ Picnic) and as you look around you see various smaller groups engaged in different conversations. These are like 'circles'. But more, because one group may be the 'Golf buddies', another group may be the 'Mission board', and one 'circle' might be 'immediate family'. This way, when you make a comment or write a note (like this one) you can direct it to a 'circle' for which it is intended. Also, a person may be part of multiple circles. An immediate family member may also be on the mission board and in your golf club.