Here is a blog from a lawyer working on open data licensing. This applies to data in general, not specifically geodata, but some of the same principles apply.
Here is a web site that contains an interesting description of the difference between open standards and open formats:
An open format is not:
Encumbered by patents.
Named using a trademark unless that trademark is usably by anyone under appropriately open terms (to define? - a trademark can be used to protect the integrity of a format, but use should not require payment, even for conformance testing)
tied to a particular software implementation (ie. it should be practical to have multiple software implementations)
An open format is:
Well and completely documented sufficient to implement a safely conformant reader/writer from scratch.
Defined in documentation that is freely redistributable (though the document may be under a license that doesn't allow changes to the spec document)
Software language independent (no dependencies on language specific components like "python pickling")
Is is desirable that an open format:
have an open source reference implementation for reading and writing.