Literary Device: Symbol

from Greek word 'symbolon' meaning "token, watchword" (applied c.250 by Cyprian of Carthage to the Apostles' Creed, on the notion of the "mark" that distinguishes Christians from pagans). Something which stands for something else - Online Etymology Dictionary

Example:

-- a poor
dry stick given
one more chance by the whims
of swamp water— a bough
that still, after all these years,
could take root,
sprout, branch out, bud—
make of its life a breathing
palace of leaves.

Function:

In Mary Oliver's "Crossing the Swamp", the 'poor dry stick' struggling to flourish in the dark swamp symbolizes the typical, simple man trying to achieve success. By using this technique of symbolism, the author was able to create an even deeper relationship between the speaker and swamp.