Players are any character with a real person in control. This could be anyone who participates in any Game, Group and more. Players are able to take part in numerous activities among the community, such as gaming, buying/selling items, earning Player Points, editing their character, and foruming.
There are two kinds of players. A permanent account, and when you log off or leave a server, your player still exists (unlike a Guest as mentioned below), unless banned or removed from ROBLOX forever. There are at least 90,552,000 accounts on ROBLOX (That's almost as twice as the population of California!) and counting. These accounts can be created through the login page and accessed by signing up on the log in area. These accounts may interact with the community depending on the chat settings set by an adult and safety measures in effect on the account. These accounts can also be banned by the ROBLOX Moderators and Administration Staff as an act of punishment for breaking rules on the player's account.
Guests, on the other hand, are players who do not have an account, an individual name, and are present only for being inside the server. Once outside of the server, the Guest does not exist and cannot interact with the community. This is the only option to playing on servers while not logged in when accessing and during the extent of the playtime. Guests cannot communicate with other players without the use of certain scripts or exploits.