On many DOS and Macintosh systems, you start right at the "root" of the filesystem tree. In effect, you start with a blank slate, and create subdirectories to organize your files.
A UNIX system comes with an enormous filesystem tree already developed. When you log in, you start somewhere down in that tree, in a directory created for you by the system administrator (who may even be yourself, if you are administering your own system).
This directory, the one place in the filesystem that is your very own, to store your files (especially thethat you use to customize the rest of your environment) is called your home directory.
Home directories were originally stored in a directory called /usr (and still are on some systems), but are now often stored in other directories, perhaps named /u or /home.
To change your
cd with no pathname; the shell will
assume you mean your home directory.
explains "nicknames" for your home directory and other users' home