\item[tail]  A command line utility for printing data from the end of a specified file or files to \texttt{stdout}. It is useful for monitoring log files.

\item[tar] A command for archiving files into tarballs. As a noun, it is also shorthand for the tarball itself.

\item[tar (tarball)] Tar is shorthand for ``tape archive.'' Although tape archives are no longer around, tarballs are a common file archive format in Linux. Tarballs are not compressed, but you can use a compression tool such as gzip or bzip2 when creating them to compress the files. The common file extension for a tarball is .tar, as in archive.tar. When combined with gzip, tarballs often take the filename format archive.tar.gz and when combined with bzip2, filenames often assume the filename archive.tar.bz2.

\item[terminal] A text-based user interface. On most Linux distros, it can be accessed by pressing \texttt{Ctrl + Alt + t}.

\item[tex] 

\item[tldr] 

\item[tmp] 

\item[top] 

\item[touch] 

\item[troff] 

\item[Tux] 

\item[Ubiquity] The default installer for Ubuntu and its derivatives.

\item[Ubuntu] 

\item[uname] A command line utility that prints basic information about the operating system name and hardware. Several options are available; for example \texttt{-s} prints the kernel name, whereas \texttt{-n} prints the system's host name.

\item[Unity] Ubuntu's desktop environment, \textit{i.e.}, the name for Ubuntu's graphical interface. A ``shell'' for GNOME.

\item[Unix]

\item[unix principle] 

\item[unzip] A command for decompressing \texttt{.zip} archives.

\item[update] To change software or parts of software to newer versions, in order to add new features, eliminate bugs, or enhance security, or for a combination of those three reasons. In Ubuntu, the \texttt{apt} (\textit{q.v.}) application handles updates.

\item[useradd] A command for creating a new user or changing (with the \texttt{-D} option) the defaults for new users. The \texttt{-G} option will allow you to add the user to comma-delimited list of groups upon creation, \texttt{-p} defines an initial password for the account, and \texttt{-U} creates a group with the same name.

\item[userdel] 

\item[usr] 

\item[var] 

\item[VI (vi)] A command line text editor. ``VI'' refers to the word ``visual.''

\item[VIM] Acronym for ``VI Improved.''

\item[wget] 

\item[which] A command which shows where an app is installed. The default usage is \texttt{which <appname>}.

\item[window manager] A layer of software that works with the X Window System (\textit{q.v.}) and provides windows management. KDE uses KWin and GNOME uses Metacity.

\item[working directory] 

\item[X (X-11, X-Windows)] A windowing system for bitmap displays which is common on Unix-like operating systems. It handles the low-level tasks for the graphical interface. We typically discuss \textbf{X-11} as the eleventh version is the one currently in use on most Linux desktop systems.

\item[xdvi] An application for viewing dvi files.

\item[Xfce] A desktop environment that is considered to be one of the most efficient in terms of resource usage, and is therefore often preferred on older machines. It forms the basis of Xubuntu.

\item[xpdf] An application for viewing pdf files.

\item[Xubuntu] A distro derived from Ubuntu that uses the Xfce desktop (\textit{q.v.}).

\item[zip] A command for compressing one or more files into an archive using the \texttt{zip} compression algorithm. 

