What does 'rgba' stand for ?

Answer 1

It's used to represent colors.
rgb becouse it contains red, green and blue colors, and a because it have alpha chanel. (this last one is use to set transparency)

Answer 2

Yes its used for that

Answer 3

RGBA stands for red green blue alpha. While it is sometimes described as a color space, it is actually simply a use of the RGB color model, with extra alpha channel information.