A yard party, usually held in the front yard of a house. Its public nature may attract passers-by to join. In the early days of the coronavirus pandemic, before stay at home orders made gatherings of this nature unacceptable to many, a yarty was a way to socialize while maintaining a 10 foot separation.

Briefly, "the realization that each random passerby is living a life as vivid and complex as your own." Originally from the Dictionary of Obscure Sorrows, which has a lot more beautiful neologism definitions like this you might enjoy.

To party without restraints, rational or morals.

A party on a yacht.