This is a term which refers to a somewhat fluid or possibly changing set of ideas. Although such thinking is subject to change, it is the best we have to go on at the moment - and in light of the inherent limitations of being human, it's not likely to get better.
Hope that's OK
LarsMarowskyBree: A philosophical precedent for this is Descartes' provisional moral code in the absence of ultimate truth. In software development, this is typically referred to as Agile Software Development or iterative development. The quintessence being to keep prepared to change your code all the time whenever we learn better, and to expose as little as possible to the users as APIs are hard to change.
(As a side note, I prattle away way too much. Be also prepared to stand that [;)].)