BUZZ!

If you mean "length", and you think that when you say "lap" that there is some chance that the listener will use the dictionary definition of lap (one circuit of a racecourse or track), then use the word length instead of defining lap as a 1/2 of a circuit.

Maybe that's the terminology that has always been used, but that doesn't make it right. Is it any harder to say "length", and does it cause less confusion? If so, then ditch the confusing term lap and use the less confusing word length.

Either that, or don't be surprised when people assume you need to get back to where you started before you can call it a lap.