The Status / About page is the third tab of the Status Information Window (menu item
Plugin > LiveTraffic > Status / Information...):
By default, only the first Aircraft / Channel status section is open.
Live aircraft shown
is the number of aircraft that LiveTraffic currently draws into your simulated sky.
Aircraft seen in tracking data
is a potentially larger number as it also includes aircraft for which some data is available in the tracking data, but it is not enough to calculate a flight path
TCAS / Multiplayer
tells you if LiveTraffic is in control of TCAS or which other plugin.
is weather information LiveTraffic requests directly from AWC. The QNH value is required to convert pressure altitude to geometric altitude.
RealTraffic, OpenSky, ADSBEx, and ForeFlight are your data channels. "Serving # aircraft" refers to the number of aircraft this channel currently drives, visible or not.
The link icon to the left opens their respective radar view so you can check coverage, or another relevant web page per channel.