To build a bit on /u/Sherbert42's answer: teleology (in a historiographical sense) is a form of historical enquiry which attempts to construct a narrative view of history as a progressive march in one direction; towards an inevitable end point.

To give one particularly notable and illustrative example of teleological thinking: look at 'Whig history', a school of thought described by Herbert Butterfield which argued that all history can be considered as an inexorable march towards enlightenment/liberalism.

The problem with the teleological approach is that it tends towards sophistry: to use the Whig history example again, the idea that British-style liberal enlightenment is the apex of human progress, and that the eventual convergence of all history on that point is an inevitability, is deeply problematic.

The idea that you can divine a perfect (or in any way satisfactory) linear narrative in history become ludicrous almost as soon as you start to interrogate it to any depth. The construction of these teleological narratives generally involves highly selective use of evidence, straw men and the complete dismissal of countervailing viewpoints or interpretations.

What always surprises me is that this prism for understanding history hasn't entirely gone out of fashion. Butterfield wrote The Whig Interpretation of History in 1931, about historians mostly of the 19th century, but Francis Fukuyama's 'End of History' theory in the 1990s owes a lot to these ideas: the idea that the fall of the Soviet Union represents the ultimate triumph of liberal democracy as "the final form of human government".

Edit: as someone else pointed out in the comments, I mangled my understanding (misread old notes from uni and clearly wasn't paying enough attention) of Butterfield's place in the Whig canon — as a critic and taxonomist, not a part of the canon. Duly corrected/now going to go hang my head in shame.

OP here, Thank you all of you for such thorough and thought provoking replies and comments.