Third party Apps?

apps not made by apple (which are the majority of their apps)

they are instead made by a developer, using the tools apple supplies for people who wish to be a developer.

It uses the coding called "swift" rather than HTML, CSS, etc.

(side note: if you want to learn swift, you can download an app called "swifty" from the app store. It's a free tutorial)

I'm sure you know about apps like snapchat, fruit ninja, kik, candy crush, facebook messenger, etc. These are third party apps.

Apps that are NOT third party are things like garage band, imovie, pages, apple store, itunes remote, and the built-in apps.

"Third party" means not developed by the vendor (Apple, in this case, as the "first part"), nor by the customer (you, in this case, as the "second party".) This is from sense of "party" as a person or group involved in a discussion, contest, contract, etc.

There is very little support for customer-developed software on phones and tablets, and most agreements and contracts don't use the "party of the first part" language any more, so "third party" is a bit like "third world" in that not many people know what the first two are or were.