Holism: The idea that there are
wholes that are in some sense more than the sum of their parts, or some
practice based on such an idea.
There is some sense in which
there are wholes that are more - or other - than the sum of their parts,
just as a building is more or other than the collection of the bricks
from which it is built, but it is difficult to spell this out in clear
and rational detail, and when this is to some extent succesfully done this will tend
to be formal and mathematical (see e.g. Simon, Woodger, or Souriau).
In such rational accounts, what makes a whole, such as the house from
its stones, beams, tiles etc. are specific
relations between the parts, that make it cohere into the
structure that forms the whole.
This one can illustrate even in geometry: What makes a triangle is
not just some gathering of three straight lines, but three straight
lines such that the endpoints of each are connected to an endpoint of
Apart from more or less mathematical theories of
wholes and systems (and indeed including
some of these: think of some expositions of "systems theory"), holism is a modern cant
term, that is used to give status and an appearance of depth to what are
in fact usually deeply nonsensical but quite possibly highly
remunerative theories, often in the social sciences or para-medicine.
In brief, when you read 'holistic' or 'holism' beware, especially if
there is no mathematics, or such mathematics as there is is beyond you.