A computer is a machine that follows a list of instructions called a program. An Android device is a computer and an app is a program.
A snippet is a short, self-contained excerpt from an app, demonstrating how to instruct the device to do something. We can re-use the snippet by pasting it into one of our own apps, possibly with some minimal changes.
One way to share a snippet is to post it on the GitHub website https://gist.github.com/. A snippet shared there is called a gist. You can then share a link to the gist with your friends.