According to the Collins Dictionary, courtesy is politeness, respect and consideration for others. The Cambridge dictionary defines common courtesy as the basic level of politeness that you expect from someone. It's really just being kind and considerate to the people around you.
You don't have to go far to find bad examples of common courtesy. We'll be looking at examples of these on the blog over the next few months. This week's common courtesy is 'don't use your speaker phone in public.' I have seen this countless times on the public transport, at the shops and at school. No one else on the train needs to hear your conversation about what happened at the party on the weekend. If you must talk on your phone in public, try to find a secluded place and hold the phone to your ear. If possible, offer to call the person back later.