Sub-neighborhood

A sub-neighborhood is a neighborhood that can't exist solely on its own.

Sub-neighborhoods exist in a sort of "time warp". No matter how long Sims spend in one, they will return home no more than a few hours after they left. It's not only possible, but common, for them to return when they left.

The Sims
Sub-neighborhoods in The Sims are often referred to as community areas. Except for Old Town and Magic Town, they contain 9 community lots laid out in a 3x3 grid. (Magic Town has 9 lots, but three are residential.)

The Sims community areas, by expansion pack, are:

Hot Date Vacation Unleashed Superstar Makin' Magic
 * Downtown
 * Vacation Island
 * Old Town
 * Studio Town
 * Magic Town

The Sims 2
The Sims 2 sub-neighborhoods, by expansion pack, are:

University Nightlife Open for Business Bon Voyage FreeTime Apartment Life
 * Académie Le Tour
 * La Fiesta Tech
 * Sim State University
 * Downtown
 * Bluewater Village
 * Takemizu Village
 * Three Lakes
 * Twikkii Island
 * Hobbies (secret)
 * Palace Of Neverending Light (secret)
 * Fortress Of Eternal Darkness (secret)

The Sims 3
The Sims 3 sub-neighborhoods, by expansion pack, are:

World Adventures
 * Al Simhara, Egypt
 * Champs Les Sims, France
 * Shang Simla, China