There are several technologies that can be applied separately or simultaneously as not to see the usual radar plane. The most effective solutions are: you give the plane (or in general the vehicle) a suitable form and shall cover the surface with a substance that reflects how much less radio frequency radar waves.
Proper form is reflecting electromagnetic waves in only a few narrow directions. Specifically, outside the aircraft consists of a small number of flat, not rounded, when the reflected waves go in several directions defined, few, only very incidentally are directed back toward the radar. Usually the direction of the radar reflection accidentally takes too little to allow the enemy to realize what device you have, in what direction and how fast you go. All you can learn it from such a reflection is, at most, that at the time there was something in the distance T D. Such information is too poor to do any good. But more often than not return any reflection or whether the radar returns for a second radar usually at that moment is oriented in another direction, so stay invisible.
Also suitable shape is one that does not contain a right angle concave, which would operate as retroreflective. Such angles concave occur for example in commercial airplanes and airplane tail between components are very easy to detect by radar, stealth planes were so different form the tail.
Due to implementation of such changes in the form of aircraft, aerodynamics, efficiency, stability, handling and other qualities are drastically reduced.
Substances that absorb radio waves are not very efficient in that it does not totally absorb incident radiation, but are much better than nothing. Usually produced in the form of paint that includes absorbent material (ferrite, carbon, etc.), or in the form of sheets that are missing from the aircraft surface.
Absorbent material may not apply on glass pilot because they are opaque to visible. The window film is applied a conductor who makes even radar waves to reflect and not directed into the cabin, where objects have complex shapes and reflections are likely to emerge in all sorts of directions.
There would be some technology, but apply less because they are more difficult and not necessarily very efficient.
Usually the term is used in connection with stealth invisibility to radar, stealth but still there are other technologies that make aircraft etc. is not visible any other methods: engine noise, emission of radio signals, gases and smoke produced by burning fuel, direct view in the visible, infrared temperature detection of different (mainly engines and gas) etc. All are stealth and tactics used by pilots to give the cameras a chance as less than, for example by flying at altitudes small or very large.
As a complement, I would add a less known: the use of coils that absorb a large proportion of radar waves. Also, in order to avoid the detection of the exhaust gas heat, use low power engines and exhaust cooling systems are arranged in such a way as to minimize their visibility. Another important aspect is stopping communication while executing tasks, thus preventing interception.
Of course there is 100% invisible plane, but returning to radar signals are ignored because operators are interpreted as “background noise”.
Parenthetically, Michael Smighelschi see story Driver who fled the country during Ceausescu, using an airplane stealth technology, while managing to not be detected by radar, flying in beating their maximum distance of 150 meters recorded.