Cydia is a graphical user interface of APT for iOS. It enables a user to find and install software unauthorized by Apple on jailbroken iPhones, iPads and iPod Touch devices. It also refers to the digital distribution platform for software on iOS accessed through Cydia software. Most of the software packages available through Cydia are free of charge, although some require purchasing.

Cydia is developed by Jay Freeman (named "saurik") and his company, SaurikIT. The name "Cydia" is a reference to the moth genus Cydia, notably the codling moth (Cydia pomonella), which eats fruits such as apples and pears.