A Laplacian filter is a type of image processing technique used to enhance edges in images. It works by calculating the second derivative of the image intensity, highlighting areas where there are rapid changes in pixel values. This makes it effective for detecting edges and fine details. In practice, a Laplacian filter is often applied to grayscale images using a convolution operation with a specific kernel. The result is an image that emphasizes edges, which can be useful in various applications such as computer vision, image segmentation, and feature extraction.