(architecture) a vertical supporting structure (as a portion of wall between two doors or windows)
"The tall stone pier divides the double window in the old library."
a support for two adjacent bridge spans
"The massive concrete pier stands between the two adjacent bridge spans to carry their weight."
A raised platform built from the shore out over water, supported on piles; used to secure, or provide access to shipping; a jetty.
"The fishing boat docked at the old wooden pier extending far out into the harbor."
In plain English: A pier is a long platform built on pillars that sticks out over water and usually has shops, rides, or restaurants at its end.
"We walked along the pier to watch the boats come in at sunset."
Usage: A pier is a long structure extending into water that serves as a docking point for boats or provides public walkways and entertainment areas. Unlike a simple dock built parallel to the shore, piers typically project outward from land on piles to reach deeper water where ships can moor safely.
The word "pier" entered English via Middle English and Old Northern French to mean a bridge pillar or breakwater. Its ultimate origin is the Latin word for stone, which traces back to Ancient Greek pétra.