Terminology
It is important to note that, while all non-competitive inhibitors bind at allosteric sites-- i.e. any site on the enzyme other than its active site-- not all inhibitors that bind at allosteric sites are non-competitive inhibitors. In fact, allosteric inhibitors may act as competitive, non-competitive, or uncompetitive inhibitors.
Many sources continue to conflate these two terms, or state the definition of allosteric inhibition as the definition for non-competitive inhibition.
Read more about this topic: Non-competitive Inhibition