It is an abbreviation for airline "passengers." You may hear the flight attendant say, "There are 124 pax on this plane." You will not normally hear this word used by people outside the airline industry. Outside the airline industry, many native speakers will not know the meaning of "pax."

*aeroplane 20 pax- 20 persons/passengers in an aeroplane, for example in my travel office we used to say: Today I've sold 2 pax for Frankfurt-Madrid plane.

i think its 1000 $ but i am not sure

It's also used for the number of guests at a table in a restaurant.

In tourism it means airplane passengers