A broken-pitch roof is a roof that changes pitch between one segment and the next. This is usually done for aesthetic reasons, but may also be found in additions to houses or outbuildings when continuing the original pitch of the roof would bring the eaves too close to the ground. (This is probably most often seen in America when a carport is added to a house). The addition of a dormer, even a very large one, would not usually be considered a broken-pitch roof, although a shed dormer might be.
To confuse matters, there happens to be a somewhat famous house (in architectural circles, at least), called the Broken Pitched Roof House. It was built by NKS Architects in Nakatsu-shi, Japan in 2010. This house traditionally would not count a broken-pitch, as the pitch changes from fairly steep at the point to quite shallow at the edges in one continuous curve. This is a pleasing effect and they deserve the attention that they have received, but I fear that they may have inadvertently changed the meaning of the term for good. Only time will tell.