Facial landmarks involve localizing key features on human faces, such as eyes, nose, and mouth. This technique is used in applications like video surveillance, computer vision, and human-computer interaction. However, facial landmark detection remains challenging due to issues including varying image quality, pose, lighting, and face shape/size. The document discusses different algorithms that can be used for facial landmark detection, including histogram of oriented gradients (HOG) and linear support vector machines (SVM). HOG counts gradient orientations in localized image regions and is robust to lighting changes, making it efficient for face detection when combined with machine and deep learning approaches.