In summary, the conversation revolves around the use of different terms for proper time and proper length in general relativity. The main reason for using a definition that does not differentiate between the two is that in general relativity, coordinate time is often not defined, and calculations can still be done without considering the distinction. However, some argue that the difference between proper time and proper length is not artificial and should still be acknowledged. Additionally, there is a discussion about the possibility of defining arc length along a null curve and the use of non-standard definitions in physics. It is ultimately concluded that using standard definitions is crucial for effective communication, especially when helping others with homework.
ah ok, I need to read more about this kind of stuff. I've just found some university websites that are pretty good. (wikipedia's explanation was pointing me in the wrong direction, by the way it was worded).