WeChat is the predominant social media platform in China. Within the WeChat app, there is an ecosystem of apps that run within WeChat, these are called mini-programs by WeChat in English. For a Chinese person speaking English, they wouldn't say that. They'd just call it an A-P-P (speaking letters individually), the same that they would call iPhone or Android apps. But these mini-programs run within the WeChat app itself.

There are a lot of them, although a lot of them are just available as separate smart phone Apps. For example, Didi is the Chinese version of Uber and can be accessed from it's own app or through a WeChat mini-program. Mobike, a bike share system, operates the same way. However there are some useful apps only available through a WeChat mini-program, like Metro (Subway/Bus) apps for major cities.