An exclamation of extreme emotion. As such, it can be used in a plethora of methods:joy, frustration, anger, thrill, et al.
The source of the usage of this word derives from the Russian Mikoyan-Gurevich aircraft design bureau, where the word was extrapolated from the name and pronounced in its native accent (with over-articulation on rolling the 'r' with the tongue).
Due to the generally 'sharp' nature of the Russian language/accent and the distinct emphasis on certain letters within, the true meaning and emotion behind the exclamation cannot be fully grasped without implementing necessary pronounciation techniques.
Example: (you are stuck in a traffic jam in the searing heat, you would like to change lanes when a space frees up right next to you, you turn your car towards the spot, when all of a sudden a boy racer snakes his way through the traffic and takes your spot, frustrated, you exclaim...)