A mask is a way to apply something to a very specific portion of an image. Masking is a way of making parts of a layer invisible. The beauty of masking is that it can make something invisible but still be able to make it visible again at any time. Before start masking in Photoshop, create a ‘Layer Mask’ so that anybody can erase something and make it visible again.
Layer MaskLayer mask is applied to give layer the control over the transparency of that layer
Alpha MaskAlpha masking is used to hide parts of an image without losing any information and to place a background image.
Transparent MaskTransparent mask is used to keep the image intact and remove all the background