Definition of lobby
In online poker, the lobby is the main window to your poker room. This is where you'll get the time, number of players online, your account balance, tables offered, alerts on upcoming tournaments, promotions, and options for setting up the software. The lobby is where you can choose to play either cash games, tournaments, sit 'n' gos, etc. The lobby will tell you if a table is free or not, the average pot size, etc. You can also receive alerts. For example, if you want to join a table that is full, you can join the waiting list. When a seat is available, you will receive a notification in the lobby that it is your turn.
The lobby in casinos or gambling halls
The lobby does not have the same function in a casino as it does in an online poker room. The functions of the lobby will be more to inform the players, much like a question booth. In a live casino, the functions are divided. You'll have the lobby to get information, you'll have the cashier to buy and sell chips, you'll have a place to reserve your seat at a table, etc.