Cydia is the digital-content store that gets installed on your device when you jailbreak it with a tool such as redsn0w, Absinthe, or sn0wbreeze. Cydia is the place that jailbreakers can search for and download third-party applications that Apple would never have allowed in their App Store, such as applications, jailbreak tweaks, themes, and much more.
Lately it has been figured that the jailbreak is "dying out" because of the lack of an untethered jailbreak solution for iOS 6. The iPhone 5, Apple’s latest iPhone, remains unjailbroken to this day, and Apple are expected to announce iOS 7 this summer. Regardless, iOS hackers pod2g and planetbeing remain diligent in their work, having made important progress along the way.
According to a recent report from Techcrunch, Saurik (Jay Freeman) reveals that based on data he has obtained over the past couple of months, Cydia has been used on 22,780,029 iOS devices, spanning from iPhones to iPod touches to iPads, and running all kinds of different iOS versions. He also notes that in between jailbreak releases, the number of jailbreaks declines until the next jailbreak release, which by then the number of initial jailbreakers always comes out higher than the previous number:
Originally Posted by Jay Freeman
It’s not much of a surprise that the iPhone 4 is the most popular iPhone to be jailbroken, considering that the iPhone 4 is so easy to keep jailbroken because of the limera1n bootrom exploit. The iPhone 4S takes second place, at 20.4%. The iPhone 3GS takes third place, composing of 11.9% of the jailbreak community. It's interesting that the iPod touch 4G isn't as popular to jailbreak as the iPhone 4, however many people would jailbreak their iPhones merely for the ability to free themselves from carrier tethering rules and to use FaceTime over their cellular network, features that the iPod touch 4G lacks, so in a way it makes sense.
Sources: Techcrunch via iClarified