whats the name of the part???

[DIMITRIS CORSA B]

i do not know the english name of this part! Also is it the only part of this thing? i think it has an inside and an outside one!
when it has to be changed?

[jordyp]

cv joint mate, its on the drive shaft. it only really needs to be changed when the rubber splits where you can replace just the rubber or if the ball bearings collapse in the inner cv joint. you can normally hear it when it does collapse