Vagrant is a tool that allows developers to create and manage virtual development environments. It allows development and testing environments to be version controlled so that the same environment is used by all developers. Vagrant uses "boxes" which are pre-built virtual machine images that developers can use to quickly set up identical environments. The document discusses Vagrant's features like easy commands to start, stop, and access virtual machines, as well as plugins and extensions that add additional functionality. It also introduces Packer as a way to build custom virtual machine images called "boxes" that can be used with Vagrant.