To use an analogy, if you open a Twitter app and scroll, you are scrolling the entire view, which is basically made up of tweet "items". Each tweet would be an "item" in this case. Each tweet has a certain way they're laid out, they have an avatar, username, content, and retweet,like buttons. These are "components".
While you can scroll through the list of tweet "items", you CANNOT scroll within a single tweet item, there is no scrollbar inside each tweet.