Pittsburgh rare (google is your friend) is described well on wikipedia:
A Pittsburgh rare steak is one that has been heated to a very high temperature very quickly, so it is charred on the outside but still rare or raw on the inside. This has the effect of intensifying the meat's flavor by cooking, without destroying the flavor of the uncooked meat. It can also produce a slightly crunchy layer on the outside that will complement the soft interior. The degree of rareness and the amount of charring on the outside may vary according to taste. The term 'Pittsburgh rare' is used in some parts of the American midwest and eastern seaboard, but similar methods of sear cooking are known by different terms elsewhere, including Chicago-style rare and, in Pittsburgh itself, black and blue.