I admit to a strong ambivalence on this term, and the various cultural formations around it. My MIT nerd tendency is to sneer (see Marvin Minsky/on holism) but I've also always had a kind of tropism towards the California systems-thinking school, where holism and systems are supposed to be objects of study in their own right.
It boils down to this: mechanists will tell you how something works, holists by their nature don't want to know, they are focused on the beauty of the mystery.
There is something frankly religious about holism and it is in tension with science, at least the MIT-engineering-flavored science I was trained in. I think at some naive level I want to deny or resolve this tension, because I find myself attracted to both poles. And I don't see any absolute reason why you can't appreciate a system or whole for what it is, and at the same time understand how it works, how it is composed and structured out of parts.
Ah OK this is an exact parallel to Buber's I and Thou. Holism is an I/Thou stance, and it implies a coherence and soul to the self and its Thou that just precludes the kind of mechanical analysis Minsky wants to do. An entirely different world, and the I is not the same I as found in the I/It world.
A more interesting mapping perhaps: if all the world's a stage and we are all players, then holism and I/Thou is how the audience and the players understand themselves, while the I/It nerds run the lights and build the sets and ensure that the mechanisms of illusion are all in working order.
Withering self-contempt. Despises itself the most for being simply withering and not annihilating, unable to give itself what it deserves due to contamination by residual sentimentality.