The NonSerializable attribute marks a variable to not be serialized.
This way you can keep a variable public and Unity does not attempt to serialize it or show it in the Inspector.
// p will not be shown in the inspector or serialized @System.NonSerializable var p = 5;
class Test
{
// p will not be shown in the inspector or serialized
[System.NonSerializable]
public int p = 5;
}