IFS (Internal Field Separator) is a Bash environment variable.
By default it is "space tab newline".
Bash will recognize either of those 3 characters as an IFS.
When you ask bash for a list, bash will use the first IFS character, space by default
arr=( Fred Barney "Mr. Slate" )
echo "${arr[*]}" # OLD IFS
Fred Barney Mr. Slate
OLDIFS=$IFS
IFS=$'\n'
echo "${arr[*]}" # NEW IFS, each element separated by newline
Fred
Barney
Mr. Slate
IFS=$OLDIFS # Remember to set it back!
# find out what the IFS is with xxd (hexdump)
echo -n "$IFS" | xxd
00000000 20 09 0a | ..|
0000003
# 20=space 09=tab 0a=newline
# Set it back to default, if you didn't save the original IFS.
IFS=$' \t\n'