"The grimy fronts of the surrounding houses were not welcoming; some of them had broken windows, glimmering dully in the light from the streetlamps, paint was peeling from many of the doors, and heaps of rubbish lay outside several sets of front steps...." (OP3)
Grimmauld Place is a Muggle street in London on which number twelve, Grimmauld Place is found (OP3). Since number twelve is hidden from Muggle eyes, the residents of the street have “long since accepted the amusing mistake in the numbering that had caused number eleven to sit beside number thirteen” (DH12).
For a more detailed explanation of its probable location, see the essay “In Search of… Grimmauld Place.”
The name may be a play on "grim old place", which as how it appears to Harry when he first sees it. -ibid