We had a party line in the late 1960’s when we first had a phone. It was cheaper line rental if you shared with a neighbour. Our phone didn’t ring if it was an incoming call for the neighbour.
Basically it meant that you couldn’t make or receive a phone call if the neighbour was already on a call. The only way to know was to lift the handset and if you heard the neighbour’s voice instead of a dialling tone. We’d quietly apologise and hang up and try again later.
We had lovely neighbours and it worked fine for a couple of years till they moved. The new neighbour used to lift the phone during our calls and think we couldn’t hear her staying on the line to eavesdrop. So my parents ended the party line arrangement and paid extra rental for a solo line.