I figured someone would say this (each bit clocked in parallel), but there are a lot of other things one can use in an attempt to quantify whether something is

I figured someone would say this (each bit clocked in parallel), but there are a lot of other things one can use in an attempt to quantify whether something is "serial or parallel" and I don't think at the highest level any of them count more than whether or not your physically sending multiple bits in parallel down multiple wires. Oh, and BTW, you can cut data lines on any number of "parallel" buses like DDR and they can frequently continue to work because there are extra ECC/parity lines which can recover the original data, or they are packetized and can recover/detect errors. Particularly on die/board level clocked interconnect buses which don't have as much complexity as the longer distance, outside the chassis interconnects. OTOH, a single serial line is done if it gets cut. You can only fix that by... ganging them in parallel. (edit: I keep tweaking this, but clock recovery isn't a hallmark of serial lines either, as there are plenty of things traditionally considered serial that have separate clock lines and have the same problems that happen on what one might consider a traditional parallel bus when run at high enough frequency)