For me, it's my mother's maiden name. On all the forms I have had to fill, both online and offline I had always erroneously entered her first name "Jane" as her maiden name instead of her father's name "Ikhile". I had my doubts I was doing the right thing all along, but it was only recently, I called her to confirm. She couldn't believe I had been making this mistake all these years, and in the end we both laughed it off. Any experiences worth sharing?

This is not really culture related, will move to appropriate section.