There are many articles on the Internet telling you what Street Photography is or isn't. It's not so much it's a hard genre to describe but that every article you read is subjective. So this is my subjective view. I see Street Photography as a form of social documentary, therefore people should be the focus of attention.
Another term often used is candid, though even here opinions vary, some folks feel that eye contact nullifies any candid moment captured. I disagree, street and candid are about capturing unplanned moments and capturing the emotion of that moment, often it's the unplanned eye-contact which makes that moment of emotion stand out.
Street photography should be unposed, though sometimes people spot you and do an impromptu pose, I would still class that as street.
Street photography does not have to be in an urban environment, it can take place on a beach, in a park or in the wilds of the countryside.
Nor does street photography have to be in black and white, often streets are vibrant with colour which adds to the atmosphere your lens is trying to capture.