Account

A player's account is similar to his or her character. While the avatar exists in-game, a player's account is used to receive messages from Jagex, post on the forums, and access the player moderator centre (if the player has moderator status, that is).

Jagex has stated that accounts and characters are generally kept separate, meaning that black marks received on an account (such as in the official forums) do not reflect on a player's character (with the exception of a ban or mute).

Accounts are often sold on "Black Markets" even though Jagex strictly prohibits this with Rule 6. Jagex keeps a strict watch on players attempting to sell accounts, and attempting to buy or sell an account is not recommended as it will most likely result in a permanent ban.

Player Character
A player character is a character controlled by a player. These characters are an icon or representation of a user in a shared virtual reality. Player characters are referred to as avatars, PCs, and sometimes they are shortened to just player.

Players are customizable, meaning you can make them look unique. With a large range of options to choose as a body, and many items to make your character look truly one of a kind.

Compare with non-player character.