Quiz: Remember the definition of mal de mer?
($IFS) A predefined environment variable in the Unix Bourne shell whose default value is the three-character string containing space, tab and line feed. Any string of one or more of these characters separates the command and each of its arguments in a command line.
$IFS also tells the shell's built-in read command where to split an input line when reading into multiple variables. E.g. setting IFS=: would be appropriate for reading a file with ':'-separated fields, such as /etc/passwd.