Classification in machine learning refers to the task of assigning the correct class (aka label) out of a set of classes to a feature. The feature (aka observation) can be e.g. an image for image classification, or a pixel for pixel-wise classification. Of course, non-visual data like audio signals or point clouds can be classified. In the field of computer vision the classification is a well known task. Many different machine learning approaches are designed for the task of classification. A model which was designed for that task is refered to as a classifier.