Probabilistic objectness is a computer vision concept and formulation that quantifies the probability that a candidate image region contains a foreground object rather than background clutter by modeling the statistical distribution of visual features. While standard object detection typically relies on discriminative classifiers that risk categorizing unannotated or novel objects as background, probabilistic objectness uses probability distributions over feature representations to evaluate the general likelihood of an object being present. By measuring candidate regions against estimated feature likelihoods, this approach enables detection models to reliably distinguish background noise from both previously seen and novel or unlabeled objects, making it particularly useful in open-world and generalized visual detection settings.