Quintilian labels allegory what is elsewhere called a "conceit": an extended metaphor:
The ship of state has sailed through rougher storms than the tempest of these lobbyists.

Allegory also occurs when an allusion is made with no introductory explanation and the speaker trusts the audience to make the connection, as in the following example, where reference is made to the historic landing of a craft on the moon, but no direct connection is made to the more mundane application of this allusion:
Well, the Eagle has landed. I thought you'd never make partner in the firm.

• metaphor
• simile
• conceit
• catachresis
• parabola
• Figures of obscuring

• Comparison