A text file is simply a normal file that happens to contain human-readable
text. There's nothing special about it otherwise. The other kind of file,
a binary file, is meant to be interpreted by the computer.

You can view either kind of file with the less file pager if you have it
installed (install it if you haven't, it's quite useful). Type less
/etc/profile to view a sample text file. Notice that you can read the
characters even if their meaning is obscure. Type less /bin/ls to view a
binary file. As you can see, the ls program is not meant to be read by
humans.

Sometimes, you'll find files that end with .gz. These files may be viewed
with zless; you can run it like so:

zless /usr/doc/ae/changelog.Debian.gz

Tip: zless is great for viewing documentation, which is often shipped in
.gz form.

The difference between the two kinds of files is purely a matter of what
they contain, unlike in some other systems (such as DOS and MacOS), which
actually treat the files differently.

Text files can contain shell scripts, documentation, copyright notices, or
any other human-readable text.

Incidentally, this illustrates the difference between source code and
binary executables. /bin/ls is a binary executable you can download from
Debian, but you can also download a text file that tells the computer how