Originally Posted by
diskus69
Thanks everyone for the replies. After some further digging It seems the terminology is "1 way release" and "two way release". They also have "multiple release" and "instant release". What I found more challenging is to find exactly which features are found on which models of shifters, especially past models.
one way release = the upshifting (to a smaller cog at the rear) is done only by pulling the index finger lever
two way release = the upshifting can be done either by pulling the lever with index finger or pushing it with the thumb
multiple release = you can upshift several cogs with one movement of the lever
instant release = the RD moves down the cassette as soon you push/pull the release lever (simultaneously with the click), as opposed to moving when the lever is released after pushing it.
The three latter options are available only on the newer/higher end shifter models, as far as I know.