Also, I assumed that BigRedBeta wasn't requiring an explanation of electives vs. sub-is but rather that often it seems like all 4th year rotations are actually sub-is rather than electives. I know I've felt that way...for example, at my school, you can't do an elective in surgery or peds or medicine. Only sub-i's. And many away rotations I've looked at refer to the rotation as a sub-i/acting internship.
Your school is not really the norm on this, based on what I have experienced/heard. At most schools at which I have contacts, there are sub-I's and there are electives during fourth year, and they are NOT equivalents by any stretch of the imagination. Most schools require you to do 1-2 sub-Is. These are where you function as the equivalent of an intern (but with greater supervision). They tend to be valuable opportunities to get good LORs for residency applications, because the attendings can give residency programs a better sense of how you will manage an actual internship, and they give the students a window into what to expect after graduation. Then there are the electives, which are much more chill, and where your responsibility is often quite limited -- these tend to be in things you didn't have third year rotations in, or where your exposure during third year was more limited (things like derm, rads, anethesia, path, ortho, optho, etc.). Lots of people try these to get a flavor of those fields, or because they want to go into them, or because some are light enough schedules to allow folks to interview or study for Step 2. So they are very different than a Sub-I as that term tends to be used. I would encourage you to talk to folks at more schools because much of what you describe is very different than what most of the schools have in place.
And I would limit your focus on terminology for "away rotations" because, as you have already demonstrated, the terminology for an away rotation tends to be confused and different than what people experience at their home school. An away rotation is an opportunity to "audition" to a program you may want to apply to. In some away rotations you will, in fact be applying to do a Sub-I at a particular school, at others it may be an elective -- it depends on the offerings of the school. For instance most of the IM or surgery offerings in 4th year may be Sub-Is, while more specific subspecialties like cardiology or nephrology may be electives, and things like derm or optho may only be electives. But in an application for an away rotation, it's a pain to talk about "sub-I or elective" away rotation so for convenience, they may call it things like an "elective clerkship", a "sub-I" and so on. But that is a catalog convenience, not a definitional term. For the most part,
at most schools a Sub-I and an elective are different things. Which is why if you go to the ERAS discussion board, you will see talk of saving one LOR space on ERAS for a recommendation from your sub-I rather than using it up with electives. A sub-I is just different, and adds more value because it tends to be more like what you will experience in residency than in third year. An elective, by contrast may be even
less stringent than a third year rotation.
At any rate this is all a matter of semantics. If you are really interested in how the terms are used at other schools, talk to people at other schools. Ignore the away rotation catalogs/applications/websites because those terms tend to be mashed together so they don't need separate language depending on whether you are applying to do a sub-I or an elective specialty there.