Neighbors are friends who you have connected with in the game. Neighbors are important to the game because you can visit their apartments for bonuses. Neighbors will also be important to your ability to unlock certain things in the game and will be helpful for sending and receiving gifts.
If your Facebook friend is playing City Girl Life, that person should be your neighbor! However, you will only see 50 neighbors at one time.
You can visit each one of your neighbors as many times as you like to earn coins, collectible items and more. Please note that your first 5 interactions with your friends are free and any additional actions after that will cost your energy. Additionally you do not receive gold for visiting neighbors.