ENY is simply an abbreviation of ENEMY. OBJ is an abbreviation of OBJECT.
The numbers associated with them are used to determine how many perk points you get for killing an enemy airplane or destroying an object.
For example, say you are flying an airplane with an ENY of 20, and you shoot down an airplane with an ENY of 10. You divide the ENY of the plane you shot down, in this case 10, by the ENY of your plane, 20, and get 2 perk points.
Now say your plane has an ENY of 10, and the plane you shoot down has an ENY of 20. In that case, you only get .5 perk points. It is a way of balancing the perk point system and the arenas, so that the less capable airplanes get some love too.
In a similar fashion, the OBJ number is used to determine how many bomber or attack points you get for destroying objects such as gun emplacements and hangers.
Generally speaking, the higher the ENY or OBJ, the more perk points you get for kills in that plane. I believe there are other factors, like how many people are on the country roster at the moment.
If you get a message that planes with an ENY of less than 9 are not available, it must mean that your country has considerable amount more players than the other countries. So in attempt to balance that, the more advanced planes are grounded.
