title: Differences between vue instance and vue component?
body: <p>I'm new to vue js and have some questions when learning it.</p>
  
  <p>I'm now a little confused about the relationship between its instance and component. As far as I learned, every app build by vue should only have one instance and one instance only, it can have as many components as you like if needed. But recently I've seen a demo, and in that demo it has more than one instance.</p>
  
  <p>So my question is, is that ok to have multiple intances in one app( the demo code works fine, but is that the correct way)? What's the best practice to use instance and component in vue app?</p>