I can't be sure, but it looks like a similar part on one of my bikes. It could be a protector / spacer that snaps on the shifter cable end and fits into a notch on the derailleur.
It isn't really necessary on my bike anyway. The bike functions fine without it. It just protects the cable where it joins the derailleur. It may help keep crud from getting into the cable end.
Could be something completely different on your Trance though.