symbolic link or soft link
A special filetype which is a small pointer file allowing multiple names for the same file. Unlike hard links, symbolic links can be made for directories and can be made across filesystems. Commands that access the file being pointed to are said to follow the symbolic link. Commands that access the link itself do not follow the symbolic link.

system call
A C language function that is used to request services from the UNIX kernel.

tcsh
A C shell–like user interface featuring command-line editing.

uninitialized shell
When a shell is started it is uninitialized. This means that important parameters required by the shell to function correctly are not defined.

usage statement
A statement issued by a shell script when one or more of its arguments are improperly specified.

utility
Utilities are programs, such as who and date, you can run or execute.

variable substitution
The process used by the shell to substitute the value of a variable, when the variable’s name is specified.

wc
The command used to count the words, lines and characters in a file.

word
An unbroken set of characters. The shell uses spaces and tabs to separate words.

write permission
Controls the users who can modify a file.