In relation to Monogatari Series, cours refer to the individual anime adaptations of the novels. In Japanese television, a cour typically describes a unit of television programming that usually contains about 13 episodes.
In traditional anime series, different cours would commonly refer to the different seasons of a series. Since the Monogatari Series anime adaptation organizes the series in seasons based off the of light novel series (such as Monogatari Series Second Season actually being the fourth cour), the cours of the series do not represent seasons of the series so much as individual adaptations (i.e. one arc, 4-5 episode cours such as Hanamonogatari or Tsukimonogatari wouldn't make sense to be considered their own "season").