Vagrant is an awesome tool for developers to get their own sandboxed environments to play with. To understand more about Why Vagrant, you could read my earlier blog post: Vagrant: An interesting approach to setup development environments FAST. But, because Vagrant does a lot of things auto-magically under the hoods, most of the times people are left confused when they want to delete or add boxes or VMs. I will try and explain the relationships between Base Boxes, VMs, Virtual Box Instances, etc in this post.
Note: The term box is loosely used by many people, and hence the confusion has risen even further.
Read the full blog on my older site: Understanding Vagrant Boxes and VMs