What is a mask in Photoshop?

In Photoshop, a mask is fundamentally a feature that allows you to hide or reveal certain parts of a layer. This tool provides a non-destructive way to control the transparency of portions of an image. By using a mask, you can blend layers seamlessly, isolate areas for editing, or create complex compositions without permanently altering the original image or layer.

Masks work by utilizing grayscale values: areas that are painted white reveal the content of the layer, while areas painted black hide it. Shades of gray can create transparency effects, allowing you to gradually transition between visible and hidden areas. This flexibility makes masks an essential part of layer management in Photoshop, enabling detailed control over how images are combined and edited.

The other options describe different functions in Photoshop that do not represent what a mask is. For instance, cropping images involves trimming the edges of a photo, effects for color enhancement relate to adjustments made to the overall look and feel of colors, and brightness settings strictly focus on enhancing or reducing the lightness within an image. Masks, however, specifically pertain to revealing or concealing parts of a layer, making option B the accurate choice.