What does linking/unlinking with Homebrew mean?

Question

What does it mean to link/unlink something with Homebrew?

Answer 1

It symlinks the installed package (located in /usr/local/Cellar) to /usr/local.

So when you type for example:

$ <name-of-binary>

in your terminal (ex. $ rvm), then the package installed via brew is run.

Answer 2

It creates a symlink from packages installed in Cellar (regular packages installed with homebrew will already be linked).

What this also does is allow the symlinked installation from Cellar to serve as a dependency for other homebrew installations (if it's required). This is explained in another post.

Also with all homebrew commands you get a description of the formulae with the --help option (e.g. brew link --help).