Is simultaneous interpreting really simultaneous?

Simultaneous interpreting as a form of conference interpretation is generally considered to have seen the light of day at the Nuremberg Trials after WWII so presumably that is where the term comes from. There is a short time lag between the speaker and the interpreter because, naturally, the interpreter needs to understand what the speaker is saying before being able to interpret it. The time lag tends to be about a half a sentence or maybe five to seven seconds. Some interpreters are comfortable with a longer lag than others. It is simultaneous as opposed to consecutive where you have to listen to the entire speech before it is interpreted, whereas in simultaneous interpreting the interpreter finishes interpreting within a couple of seconds from the moment when the speaker finishes their speech. With no time lag at all, we'd have to be mind readers too.

Roderick Jones, in his book Conference Interpreting Explained, actually refers to sim as semi-simultaneous, arguing that simultaneous interpreting is a misnomer. OP, I don't think you will be able to find just one person whom we could credit for coining the term 'simultaneous interpreting'.

One of SI theories argues that SI is not quite simultaneous.

According to some research, during SI:

42% - both are talking 12% - both are silent 18% - speaker 28% - interpreter ie interpreter has a chance to speak alone almost 1/3 of the time and should use speaker pauses as much as possible.

Also, besides physical pauses there are what I call "semantic pauses" when there is no or little useful information to interpreter. There should be used as well.

Actually, it isn't called "simultaneous" because speaker and interpreter are simultaneous (which, in fact, as all of the above explain, they are not) but because the interpreter is simultaneously listening and speaking. At least, that is what my research showed when I wrote my bachelor thesis- happy to be corrected should this be false.