escaping
Escaping a character means to put a backslash (\) just before that character. Escaping can either remove the special meaning of a character in a shell command or it can add special meaning as we saw with \n in the echo command. The character following the backslash is called an escaped character.

execute permission
In UNIX, only those files that have execute permission enabled can run.

exporting
A variable is placed in the environment by exporting it using the export command.

expression
A piece of code that are evaluated to produce a numeric result, such as 0 or 1. Some expressions that involve mathematical operations can produce other results.

field
A set of characters that are separated by one or more field separator characters. The default field separator characters are Tab and Space.

field separator
Controls the manner in which an input line is broken into fields. In the shell, the field separator is stored in the variable IFS. In awk the field separator is stored in the awk variable FS. Both the shell and awk use the default value of Space and Tab for the field separator.

file descriptor
An integer that is associated with a file. Allows you to read and write from a file using the integer instead of the filename.

filesystem
A directory structure contained within a disk drive or disk area. The total available disk space can be composed of one or more filesystems. A filesystem must be mounted before it can be accessed. To mount a filesystem, you must specify a directory to act as the mount point. Once mounted, any access to the mount point directory or its subdirectories will access the separate filesystem.