command separator
Indicates where one command ends and another begins. The most common command separator is the semicolon character, ;.

command substitution
The process by which the shell executes a command and substitutes in the output of the command.

comment
A statement that is embedded in a shell script but should not be executed by the shell.

complex command
A command that consists of a command name and a list of arguments.

compound command
A list of simple and complex commands separated by the semicolon character, ;.

compound expression
Consists of one or more expressions.

conditional execution
Alters the execution of a script, based on the system type. A script that uses conditional execution usually consists of an if statement at the beginning that sets variables to indicate the commands that should be used on a particular platform.