Concepts

The four words the commands and their refusals are written in.

Four words carry the whole tool. The commands and their refusals are written in them.

WordWhat it means here
CanonicalThe checkout that clones are made from. It is an ordinary git checkout that nobody works in: it sits on the line you branch from, its dependencies are installed, its submodules are initialised, and its working tree is clean.
CloneA copy of the canonical, on its own branch, in its own directory beside it.
AddressEverything inside a checkout that records where the checkout lives.
Shared blocksTwo files on the same filesystem holding the same storage until one of them is written to.

From source

Building it from a checkout of the repository.

Canonical

The checkout that clones are made from. It is an ordinary git checkout that nobody works in: it sits on the line you branch from, its dependencies are installed, its submodules are initialised, and its working tree is clean.