What is "Transparency" in the Computer?
Transparency means you can see through something. The antonym is opacity. In the context of image editing and digital graphics, an image has transparency if some of its pixels are not fully opaque, i.e. they are transparent or semi-transparent.
Transparency is often symbolized by a checkerboard pattern. For example, when viewing an image in an image viewer, a checkerboard pattern background behind the image may indicate what areas of the image are fully transparent or semi-transparent.
For the computer to make use of a transparent image, it must be blended with what is behind it. The blending function used for this is very simple and well-known, and in it the degree of opacity is also called alpha, which is the "A" in RGBA.
Not all image formats support transparency. JPG, for example, doesn't support transparency. GIF only supports fully transparent or fully opaque pixels, and not semi-transparent pixels. Dithering can be used in pixel art to achieve a semi-transparent effect in this case. PNG supports only lossless transparency. WebP supports lossy transparency.