That little nod to a Dylan Thomas poem that you sneaked into your PowerPoint presentation? That was an allusion, a quick reference to something that your audience will have to already know in order to "get."
An allusion often references a famous work of art or literature, or to something from your own life. For example, you might say, "I obviously am no expert at love" — an allusion to your failed relationships. The main thing to remember is that an allusion is a brief hint or a quick mention. It’s meant to bring to mind a particular subject, but it always avoids getting into it in great depth.