1) In special relativity, the proper length of an object moving at velocity close to that of the speed of light is its length as measured by an observer in the rest frame of the object.

2) A massive shit.
1) Will: Dude, that 30cm ruler travelling at the speed of light looks to be only about 28.5cm.
Nathaniel: Yeah, that's because it's proper lenth is 30cm.

2) Nathaniel: Dude, I just crimped out a proper length.
Will: Yeah, thats a proper brown length.
by justabusta January 22, 2011