unix - What does "<<<" mean on a bash command line? And where is it documented?

Question

What does <<< mean in this command line?

bc <<< "1 + 1"

It doesn't seem to a combination of < and <<, and I can't find documentation for it. It seems to behave just like

echo "1 + 1" | bc

Also works in ksh, but not in sh.

Answer 1

It introduces a here string, documented near the end of the section on input and output redirections. A here string is just a one-word here document:

bc <<< "1 + 1"

is equivalent to

bc <<EOF
1 + 1
EOF