struts vs. shocks?

What is the difference?

I am looking to buy a used jetta and the rear struts need to be replaced to have the car safetied, every place I call for part says I need rear shocks, not struts.


the car is lowered with a H&K kit if that makes a difference?


http://www.mopartsracing.com/parts/pt/strut.jpg

http://www.roadandrace.com.au/parts/parts/images/Rear%20Suspension%20Biturbo%20gas%20shocks.jpg


look very similar,,,help?