It's more likely to be a literal phrase referring to the space beneath a boardwalk, a raised wooden structure built along a beach or waterfront.
However, it's often associated with:
* The Jersey Shore: The phrase is famously used in the song "Under the Boardwalk" by The Drifters, which evokes the carefree summer vibes of the New Jersey coastline.
* A sense of relaxation and fun: The boardwalk itself is often seen as a place for leisure and entertainment, so the phrase "under the boardwalk" can evoke those feelings.
If you heard someone using "under the boardwalk" in a metaphorical way, you'd need more context to understand their intended meaning. They might be referring to:
* A hidden or secret place: Someone might say "Let's meet under the boardwalk" meaning a secluded spot.
* A place for casual encounters: Similar to above, it could imply a place for informal or clandestine meetings.
Ultimately, the meaning of "under the boardwalk" depends on the context and the speaker's intention.