alpha channel

Etymology
Coined by and  in the 1970s. Smith writes: "We called it that because of the classic linear interpolation formula $$\alpha A + (1-\alpha)B$$ that uses the Greek letter $$\alpha$$ (alpha) to control the amount of interpolation between, in this case, two images A and B". That is, when compositing image A atop image B, the value of $$\alpha$$ in the formula is A's alpha channel.

Noun

 * 1)  A numerical value specifying a level of translucency to be applied to a colour.

Translations

 * Finnish: alfakanava
 * Portuguese: canal alfa