The terms Free Software and Open Source Software are cumbersome to use, especially when speaking with laity.
Free Software seems to often need an extra qualifier "free as in freedom" (as opposed to "free as in beer"). Without that qualifier, it can have a negative connotation, as people confuse it with Freeware, which is (was?) often thought of as something gratis, but of lesser function or quality than commercial offerings.
Open Source Software has the word "source" in the middle that needs extra explanation for many people. It would be much simpler to explain Open Software, without all the source (or sores, as Hani Suleiman would say). With the emergence of Open Source Hardware, where source can have a somewhat different meaning, I think Open Hardware would also be a better fit.
Simply open is good. And it can more easily include other qualities we've come to associate with, but what the words "open source" don't actually cover: open development, open processes, open attitude. It can include both Free Software and Open Source Software, and hopefully better associations with "open software" would form in people's heads, like: it's transparent, you can take it apart, modify it, distribute it and be part of it.
So, if you agree with me, lets start using the term open software from now on. :)
PS. Lets not even speak of alternatives like Free/Libre/Open-Source Software (but don't forget to FLOSS!)