Meaning that you can film anywhere that people do not have a reasonable expectation of privacy. That means the bathroom, dressing room locker room etc.
However in a common area such as a public street or a living room you can film it.
It is legal BUT only if everyone knows that the AUDIO is being recorded.This is a sensitive thing.If you never told them that they were being audio(and video) recorded then you can not use that tape in court.That tape does not have legal value.
I think it's becoming illegal in the u.s which is redicoulous
But anyway it's part of the wiretap law and all the people being recorded have to give concent to be recorded
But make sure with your state laws