The answer is:https://technet.microsoft.com/en-us/library/cc754272.aspx
By default, Remote Desktop Services allows users to disconnect from a
remote session without logging off and ending the session. When a
session is in a disconnected state, running programs are kept active
even though the user is no longer actively connected.
To understand Remote Desktop Sessions
When a user logs on to a Remote Desktop Services–enabled computer, a
session is started for the user. Each session is identified by a
unique session ID. Because each logon to a Remote Desktop Connection
(RDC) client receives a separate session ID, the user-experience is
similar to being logged on to multiple computers at the same time; for
example, an office computer and a home computer.
Each remote desktop session is associated with an interactive window
station. The only supported window station name for an interactive
window station is "WinSta0"; therefore each session is associated with
its own "WinSta0" window station. There are three standard desktops
for each window station: the Winlogon desktop, the screen saver
desktop, and the interactive desktop.
The user associated with the interactive window station for a session
is known as the interactive user. On a Remote Desktop Connection (RDC)
client there can be multiple interactive users in addition to the
interactive user on the Remote Desktop Services console. To retrieve
the identifier of the session currently attached to the console, use
the WTSGetActiveConsoleSessionId function.
When a user logs off from a Remote Desktop Connection (RDC) client,
the session that the client has on the Remote Desktop Session Host (RD
Session Host) server (formerly known as a terminal server) is deleted
and the window stations and desktops associated with that session are
removed. However, because the Remote Desktop Services console session
is never deleted, the window stations associated with the console
session are not deleted. This affects how applications behave in a
Remote Desktop Services environment when they are configured to run in
the security context of the interactive user, also known as the "RunAs
Interactive User" object activation mode.