The following is adapted from older content contributed by anonymous trolls in 2004. It has been only slightly modified.
A parametric license is a license either mechanically generated or chosen from options and fill-in-the-blanks. The Creative Commons Open Office extension for instance makes it easy to choose a CC license based on such input(s).
Commodity markets rely on many such parametrized contracts. The Creative Commons regime has relatively fewer options. Legally, a distinct specific license emerges when the blanks are all filled in, and it may not necessarily be as easy to understand or enforce as all the other possible licenses generated or chosen, though that would be an ideal outcome for most users.
There is nothing preventing future Creative Commons licenses from having genuine blanks or options, though they should be numeric or chosen from short lists whose combinations can be handled predictably without requiring anyone to seek permission. The CCplus and CC0 protocols are attempts to move in this direction.
Open Source originated due to the demand for some options that free software did not allow for. Partly in response to this, even the GFDL has some ability to vary conditions, for Invariant Sections, Front-Cover Text and Back-Cover Text in particular. Strangely, some people object to these parameters as somehow being reflective of a lack of freedom, although its not clear why they want or need the "freedom" to alter authorship, institutional affiliations, at will. It's a common confusion to believe that free sofware and open source are merely differentiated by marketing approach. This is clearly not true. Free software is share alike and open source clearly is not. Creative Commons uses the copyleft symbol for share-alike to help make this clear to legally naive users.
A more real-world pragmatic approach would rely more on parametric licenses drawing on constraints from the real legal and political world, e.g. green license, peace license, human rights license, science license or guild license.
Current options won't work. For instance if someone refuses to give their work for free to the Pentagon they cannot write Free Software or "Open Source" or even use CC-by-nc-sa - but they can write Common Content sharable among a smaller group, which we might call guild content as opposed to open content. So what we have in Creative Commons Public License is a base of correct decisions from which to strike out in a different Share Alike focused direction, not the dead end of "open source" which just created issues with proliferation of versions and licenses and never brought in shareware, guilds or unions, or the nonprofit groups that only want to share with each other.