When said about a person: He thinks he's the center of the world. He's self-important.When said about a city: It's the center of activity.
SOURCE: Stutchkoff, Der Oytser fun der Yidisher Shprakh.
ער איז דער פּופּיק פֿון דער וועלט.
Er iz der pupik fun der velt.
He's the bellybutton of the world.