The problem with this idea when applied to this case is the motivations of people wishing to use some alternate definition. There is a real profit motive in being able to call stuff "open source" when it doesn't grant its users the same kind of freedoms the BSD or the GPL license, etc, do.
If you allow stuff like "shared source" to be called open source, you reduce the term to a meaningless buzzword, like how the term "open" is frequently abused.
citing trademarks is a heavy handed approach, but many parties with a profit motive don't care about anything except strict legality.
This is relevant in particular to this blog because Microsoft has a history of attempting to change what the term means
If you allow stuff like "shared source" to be called open source, you reduce the term to a meaningless buzzword, like how the term "open" is frequently abused.
citing trademarks is a heavy handed approach, but many parties with a profit motive don't care about anything except strict legality.
This is relevant in particular to this blog because Microsoft has a history of attempting to change what the term means
http://opensource.org/node/280