HD Visual Effects are digital post-production techniques used to enhance or alter live-action footage. They can be used to create realistic and imaginary environments, characters and objects. They can also be used to simulate realistic or imaginary phenomena such as explosions, fire, smoke, water, and other dynamic elements. They are created using software such as Adobe After Effects, Houdini, and Cinema 4D, and are widely used in film, television, and video game industry to enhance the visual experience.