Proper Length

The proper length is the length something has when measured in its own frame of reference.

Relativistic Length

The relativistic length is the length something has when measured in a frame of reference in which it is moving.

Proper Time

The proper time is the time measured by identical clocks all when measuring in their own frame of reference. That is the difference between measuring and observing, one of the central points of Einstein's 1905 paper.

These concepts will be more fully explained  on my University of Arkansas home website. It can be found at

http://comp.uark.edu/~davewall/Molly.htm

Hope to see you there!