a city: a walled, settled population center, and by extension the community that lives in it
At its core this is the ordinary word for a town or city, a fixed and usually fortified settlement large enough to have its own name, gate, and public life. It is the everyday backdrop of the Gospels and Acts: Jesus moves from city to city, the message is carried into one city after another, people are born in, sent to, and driven out of cities.
Because a city is its people as much as its walls, the same word slides naturally into standing for the inhabitants themselves. When the whole city comes out to meet someone, it is the crowd, not the buildings, that is meant.
The word also carries real theological weight in the New Testament, especially in Hebrews and Revelation. Jerusalem is the holy city, the city of the great King. Beyond it stands a coming city with foundations, the heavenly Jerusalem that is the true homeland of God's people. Set against that hope is the great city, the proud center of human power in rebellion against God. So one plain word can name a market town in Galilee, the place God chose for his name, the eternal dwelling believers are traveling toward, and the doomed empire opposed to it.