What does "a" in the rgba stand for?

Question

rgba question

Answer 1

RGBA color values are an extension of RGB color values with an alpha channel - which specifies the opacity of the object. An RGBA color value is specified with: rgba(red, green, blue, alpha). The alpha parameter is a number between 0.0 (fully transparent) and 1.0 (fully opaque).

Answer 2

alpha

Answer 3

It stands for opacity.
instead of writing
color:rgb(255,0,255);
opacity: 0.1;
you simply write
color:rgba(255,0,255,0.1)