Contains the Internal Field Separator string that bash uses to split strings when looping etc. The default is the white space characters: \\n (newline), \\t (tab) and space. Changing this to something else allows you to split strings using different characters:

IFS=","
INPUTSTR="a,b,c,d"
for field in ${INPUTSTR}; do
    echo $field
done

The output of the above is:

a
b
c
d

Notes:

• This is responsible for the phenomenon known as word splitting.