Of the intellectual virtues open-mindedness is probably the most difficult to define because it is very much a moving target. Traditionally, open-mindedness is thought to be possessed when a person sets aside his or her biases so that a judgment can be made free of prior beliefs. For example, if I were to make a judgment about the chances of the St. Louis Cardinals (my favorite baseball team) winning the World Series, in order for me to make this judgment in an open-minded way I would need to try and set aside my thought about the Cardinals.
The difficulty with a view like this one is that contemporary research tells us “setting aside” our biases may be next to impossible (see e.g. Kahneman 2011). It may well turnout to be the case that there is no such thing as being truly “impartial”. All of us view the world through our own unique lenses that have been shaped by experience and nature. Once we acknowledge that our “glasses” are just one pair of many we can be open to the opinions and criticisms of others.