Candid street photography is a sub-genre of street photography.
I spent two hours doing a candid street photography challenge.
The basic principle is that you document a scene with your camera, without interfering with your subject.
When you look at the legendary street photography Henri Cartier-Bresson you will instantly notice that he’s often very far away from his subject and unaware of the photograph being taken.
On the other hand, you have people like William Klein who’s photos I really related to, and he usually interacts with his subject and tends to do a lot more street portraits in color and black and white, than candid photography.
I’d consider both gentlemen as street photographers, since both of them have mastered how to take pictures of strangers, in each their own way.