An aircraft carries three kinds of name, and they are easy to confuse. The callsign is what the flight goes by on the radio and on the map — often an airline code plus a number (e.g. “BAW123”) or a private tail call. It belongs to the flight, not the plane, and can change trip to trip. The ICAO 24-bit address is a unique hexadecimal code burned into the aircraft’s transponder — one airframe, one address, for the life of the registration. The registration (or tail number) is the visible alphanumeric ID painted on the fuselage.
Altitude is usually given two ways. Geometric altitude is height above the ellipsoid from GPS; barometric altitude is derived from air pressure and is what air-traffic control uses. Above a transition altitude, aircraft express barometric height as a flight level — FL350 means about 35,000 feet on a standard pressure setting. Two aircraft “at FL350” are vertically aligned even if their true heights differ slightly.
Speed on the map is ground speed — how fast the aircraft moves over the earth, which FlightGlobe reports in metres per second (m/s). It differs from airspeed because of wind: a strong tailwind can push ground speed well above the speed of the aircraft through the air, while a headwind drags it below. Track is the direction of travel over the ground; heading is where the nose points, and crosswinds can make the two differ.
The transponder also broadcasts a four-digit squawk code assigned by controllers. Three are reserved worldwide as emergencies: 7500 signals unlawful interference (hijack), 7600 a radio-communication failure, and 7700 a general emergency. Seeing one of these on a tracker can look alarming, but codes are sometimes set by mistake and quickly corrected — treat them as a prompt to look closer, not a confirmed event.