Here is a link to a photographers website that in my mind shows what 'street' photography can be. The photographer is a little known Chicagoan, whose work was sold off at auction of an unpaid storage locker, when she died. The work was purchased by a History buff-Realtor ( John Maloof ), and thereby discovered.
She roamed the streets of Chicago, New York, and traveled extensively. Almost all her life she was employed as a 'nanny' and very little is known about her personal life...but her photographs. Here's the link: It's really worth taking a look.
http://www.vivianmaier.com/