Hello. Yes, these terms are used when describing the vertical positions of airplanes. Let’s first look at the definitions of Transition altitude, Transition level and Transition layer.
Transition Altitude. The altitude at or below which the vertical position of an aircraft is controlled by reference to altitudes.
Transition Layer. The airspace between the transition altitude and the transition level.
Transition Level. The lowest flight level available for use above the transition altitude.
(ICAO, e.g. Doc 4444: PANS-ATM & Doc 8168: PANS-OPS).
As you can see in the chart above. If aircraft are flying below the Transition Altitude during their climb, they will fly with the local QNH value and when the aircraft enters above Transition Altitude, they set the Standard pressure 1013.2 hPa. Similarly, when aircraft go below the Transition level during descent, they change the standard pressure value 1013.2 hPa, and set the local pressure value.
What is Altitude?
Altitude is the vertical distance of an object measured from mean sea level.
“In the US and Canada, the Transition Altitude is fixed at 18000 feet and the airspace above is known as the Standard Pressure Region” – skybrary