hi you are most likely too young to know...it is where 2 house holds shared the same phone line...basically when you made a call and then ended it the other person could then use their phone...the only thing was if you picked up your receiver while the other person was having a conversation you could hear what they were saying and likewise they could listen in on your conversations...it went on trust but if you had a nosey 2nd party privacy was not always given

think ive got that about right...
lyn