When you allude to something, you don't identify it or mention it specifically. If you allude to the fact that a cop is sitting right behind you, your friends might stop talking about their plans to rob a bank.
Allude is from Latin allūdere "to play with, joke" from the prefix ad- "toward" plus lūdere "to play." The corresponding noun is allusion, which is often used of an indirect reference in literature: Helen, a fitting name for a woman of great beauty, is an allusion to Helen of Troy.