Single origin is a term used when all the coffees for a product are gown from within one country. Think of Single origin as a geo-political certification. This is to differentiate against coffees that are blends of various origins.
Many folks believe that within the single origin definition, the roaster can blend coffees from different regions, altitudes, qualities or processes. Other use single origin as a synonym for micro-lot or estate coffee. I personally believe in the former and try to correct those that use the latter definition.
We as an industry need to be clear and consistent or the consumer will be confused and not sure of the right purchase for themselves.
It's interesting to me that in espresso terminology, SO just means "not a blend". Which is interesting since it can be a blend of coffee's from the same region via a co-op. The coffee coming from Ethiopia since the commodity exchange is now homogenized into generic "yirgacheffe", "sidamo", "harrarr", etc. Would those be considered single origin? It's sort of like saying "beer from wisconsin". Ultimately direct trade is the only guarantee of where your coffee comes from specifically.
In practice i also use the term "single origin" to describe coffee's from the same region. They could be from a few different farms in that region though.
I would agree that over time the term "Single Origin" has moved from being a fairly broad stroke definition a decade back. Our compeny likes to work our labeling and descriptions of coffee in line with what the wine industry is doing in NZ. That is the Origin (or in coffees case the Singale Origin) is the region, we then sub-classify the district and/or small holder coop. I think the general origin "ie Mandehling" or "Bali" defines the measurable region the coffee comes from, then to add Desa Nangka or Blue Batur pins the coffee down to a very measurable area of where it has actually come from. I like to think we all want to learn and teach as much about the origins as we humanly can. Being able to sharpen the lead of the pencil to as sharper point as possible really helps the customer have some affinity with the coffee, more of an understanding. In saying that I still see some shocker SO definitions of growing regions in Indonesia- especially refering to Sumatran and Java growing regions. I seem to remember that the SCAA was working on a super detailed map of origin producer countries and the regions within... with the new site cant seem to find the link.