The phrase "erroneous idea" means having a mistaken or wrong belief or understanding about something. It refers to a thought or concept that is incorrect or not based on accurate information. Full definition
One of the things I've noticed and have mentioned it to a couple of people today is the obviously erroneous idea that our thoughts must be static. (nakedpastor.com)
It's erroneous ideas like this that contribute to falling vaccination rates, since these people are being convinced that breastmilk IS a vaccine. (skepticalob.com)
There is also the non Christian erroneous idea thet we can be saved by being good or less bad than someone else. (religion.blogs.cnn.com)