A plaque is a thin piece of polished granite, also called a panel or tablet. They are available in various sizes and in all standard colours. Sizes and colours can be dictated by the council for the cemetery you are installing in.
Most cemeteries have any area to install a plaque remembering your loved one who has been cremated, no matter where the ashes have been spread.
We can sometimes also set plaques on older family monuments. These are generally made from the same colour granite if it is still available and the inscription style matched.