See Hasidic Sects.
The Haredi Jews are known as the most conservative Jews on earth, they are the Ultra-Orthodox. Though, most followers of this sect do not like that term, and prefer Haredi, Hasidic, Torah Jews or simply Orthodox.
The most important aspect of the Orthodox Jews is that they believe in two forms of the law, the written law (Torah she-bi-khtav) and the oral law (Torah she-ba'al peh) which is just as important. Both laws are followed strictly.
The most obvious distinction of these people would be their obvious clothing. Many communities of these Jews still dress as they would have in 18th and 19th century Europe with dark colored clothing, hats, long skirts and long sleeves. From the outside, it is easy to spot the ultra-orthodox. Another distinction is the refusal of electricity on the Sabbath, many Haredi families sit in the dark on Saturdays.
Where did they come from? Well, it started in Europe when the separation between Jew and gentile was more profound. During the Enlightenment, many liberals called for the mixing of cultures in the new societies that were emerging, suddenly Jewish culture was no longer "scary and weird", it wasn’t something to be outcasted. Jews were finally able to join society and culture without being feared. In response to this, many people clung even tighter to tradition and Jewish law, these people are today's Haredi. Simple as that.
Next time you are driving around the city on a Saturday afternoon and you see groups of people walking around in black, you will understand who they are and what they are doing.
In Pittsburgh, the Jewish center is in Squirrel Hill.
In Cleveland, they are on the east side, probably in University Circle.