Remote access is just what it sounds like -- the ability to access your computer from a remote location. Programs allow users to control remote computers from their local machine. In order for a remote access connection to take place, the local machine must have the remote client software installed and the remote machine must have the remote server software installed. Also, a username and password is almost always required to authenticate the connecting user.
A remote user is someone who works on a computer from a remote location. User might be able to connect to his work machine from his home computer and grab the file.
A roundel in heraldry is a disc; the term is also commonly used to refer to a type of national insignia used on military aircraft, generally circular in shape and usually comprising concentric rings of different colours.