Look at this:
% zsh -f zsh% PS1="%~%% " ~% hash -d zsh="/usr/src/zsh" ~% cd ~zsh ~zsh% pwd /usr/src/zsh
Nice, isn't it?
This way you can give names to directories, that you visit often. It even looks nice in your prompt.
This isn't strictly an alias, but you can think of them as aliases.