Understanding what weight sharing is in convolutional neural network

A CNN has multiple layers. Weight sharing happens across the receptive field of the neurons(filters) in a particular layer.Weights are the numbers within each filter. So essentially we are trying to learn a filter. These filters act on a certain receptive field/ small section of the image. When the filter moves through the image, the filter does not change. The idea being, if an edge is important to learn in a particular part of an image, it is important in other parts of the image too.