According to Wiki:
Penny dreadful is a pejorative term used to refer to cheap popular serial literature produced during the nineteenth century in the United Kingdom. The stories themselves were reprints, or sometimes rewrites, of Gothic thrillers such as The Monk or The Castle of Otranto, as well as new stories about famous criminals. Some of the most famous of these penny part-stories were The String of Pearls: A Romance (introducing Sweeney Todd), The Mysteries of London (inspired by the French serial The Mysteries of Paris), and Varney the Vampire. Highwaymen were popular heroes; Black Bess or the Knight of the Road, outlining the largely imaginary exploits of real-life English highwayman Dick Turpin, continued for 254 episodes. Other serials were thinly-disguised plagiarisms of popular contemporary literature. The publisher Edward Lloyd, for instance, published a number of penny serials derived from the works of Dickens entitled Oliver Twiss, Nickelas Nicklebery, and Martin Guzzlewit.
But what is the significance of the title related to the series? Is the script the reprint of different scripts or is it having some other significances and why Penny Dreadful only?