The Path of Skillful Means

Skt., upayamarga
Tib., thabs lam

In general, thabs lam seems not very different from zab lam, considering that one can use both these phrases when making reference to the major teachings of Naropa:

a. thabs lam na ro'i chos drug = the path of means as the Six Doctrines of Naropa
b. zab lam na ro'i chos drug = the profound path of the Six Teachings of Naropa

Yet there are some uses of the term thabs that illuminate certain aspects of these teachings more clearly than zab does.

In order to understand thabs, thabs lam, and its various derivatives, it is good to recall that lam translates as "path" and/or "way" (Skt., marga), whereas thabs stands for "means", "skills", and/or "skillful means" (Skt., upaya).

Now considering what we know of the term thabs dang shes rab (Union of Skillful Means and Profound Cognition), it is most interesting that thabs shes is given as a synonym for thabs lam in dictionaries.

This hints at the fact that The Path of Skillful Means (thabs lam) is actually - without showing it with so many words - once again a path of combining/uniting Skillful Means (thabs) with Wisdom or Knowledge (shes); a union that is also known as thabs shes kha sbyor.

What is most interesting in this pursuit to reveal the "deep secret" of Zaplam is the fact that both Maha Yoga and Anu Yoga teachings refer to two different paths of means, and in both cases the difference between the two paths depends on using the so-called "upper door" or "lower door" of the body. The name for these Anu Yoga teachings clearly shows this:
thabs steng sgo'i man ngag dang 'og sgo'i man ngag gnyis. Literally, this says:

and can best be translated as The two secret instructions concerning the skillful means of employing the upper and lower doors of the body.

And what are these steng dang 'og sgo gnyis, the two upper and lower doors of the body?

Last not least, looking at a few more phrases associated with the lower doors,

the wheel/chakra of sustaining bliss at the secret organ (gsang ba bde skyong gi 'khor lo)
great bliss of the lower gate ('og sgo bde chen)

we're all of a sudden back to the union of bliss and emptiness discussed in connection with the spelling zab lam. Here, united in the yab yum position, both the male consort (yab) and the female consort (yum) merge their two secret spaces (mkha' gsang gnyis) on the path of interdependence ('khor ba'i lam) in order to achieve liberation from the dualistic fixation (gnyis 'dzin) in which perceiver and perceived seem different entities.