Opacity map vs transparency map : when to use which?

[loganb]

It seems like there are 2 ways to get transperency form an image texture:
Opacity map or transparency map.

 What's the difference between these?
Why would you sue one and not the other?

[loganb]

No answer...Let me rephrase :

Is this correct:

Opacity map is for objects/ images with translucent borders that are "hard" ,
either a pixel is completely opaque or it's completely transparent.

Transparency map is for objects/ images with translucent borders that are "soft",
pixels varying gradually between opaque and transparent

do I have it correct?

[joojaa]

no, opacity is one channel, and inverse in meaning of transparency. Transparency describes the medium, and may have a color..

[andy-davis]

I've never thought about this one before, but now you mention it, I'm confused too!
So is transparency just a way of individually controlling the opacity of the R, G and B channels?
And in what way is it the opposite to opacity?