An epic simile is a long, carefully developed comparison that stretches beyond a single quick image. Instead of briefly saying one thing is like another, it builds the comparison in several linked details, often to slow the pace and make a scene feel grand, vivid, or dramatic. Epic similes are especially common in long narrative poems and are sometimes called Homeric similes.
Example
The warrior charged across the field
like a storm rolling over open water,
its dark front widening, wind-driven,
thunder gathering in the clouds,
then crashing down with flashing rain.