In rural areas where phone lines had not yet reached full penetration, party line service was offered as a subscription. These were lines that serviced anywhere from 5-20 households. Each subscriber had their own dedicated ring.
At our house, one long ring followed by two short rings meant a call was coming for us. A neighbor would have a different ring sequence, so you didn’t answer those.
Since it wasn’t a private line, if you picked up the phone you could listen to others’ conversations. Etiquette said that if you broke into the conversation to announce you had to make an urgent call, the other parties would wrap up their call.