All passengers in your airport, both arriving and departing, have various psychological needs which should be catered to. Passengers will attempt to accomplish their need if the activity is possible. If not, their need will increase.
You can view average passenger needs by hovering over the Passenger Satisfaction button along the top of the screen. The tooltip will display a list of all needs, in ascending order from the least to most satisfied needs. Beside each need is a percentage value, representing the percentage of passengers who are satisfied in this need. A value of 100% means that all of your passengers are satisfied with the need.
You can also view an individual passenger's needs by hovering over the passenger. The list of needs will be displayed in descending order from the most to least required needs. Passenger needs are measured as floating point values between 0 and 1. If a passenger's need is 0, it means that their need is completely satisfied. On the contrary, a passenger need value of 1 means that it is desperately desired.