the.com/block party

means A street closed to cars so the neighbors who live along it can fill it with food, music, and folding chairs instead.

from Straightforward compound: 'block,' the urban unit of a street between two cross-streets (a usage that took hold in American English as cities were laid out in grids), plus 'party.' The institution grew alongside 20th-century American neighborhood life, often formalized through city permits that let residents barricade their own block for a day — bureaucracy briefly in service of a cookout.