Carry-on approved will meet most airline Requirements for luggage allowed onto an airplane ; small enough to FIT under the  seat or in the  Overhead bin. Standard size is 56 cm long, 35  
cm wide and 24 cm deep. (In other non-metric systems:  22 x 14 x 9 inches) 
Other definition:
Carry-on approved is the  Will meet most airline requirements for luggage allowed onto an airplane; small enough to FIT under the  seat or in the  overhead bin. Standard size is 22 x 14 x 9"
 
    
        
                                        