Citrix Receiver is a platform or container to host other web based programs and can share desktops and presentations. It will allow participants to view (and share as desired) desktops, communicate via message board and other things. The most likely way you got it was by participating in a webinar of some type. For me, it's one of those necessary evils. It usually just works though.

You should be able to just go to the Windows installed programs list and uninstall it. If you ever need it, you'll end up with it being installed again.