There's "hard real time", where a system must respond within a specific time (eg. vehicle or rocket control, or PLC systems you mention, etc) and "soft real tim

There's "hard real time", where a system must respond within a specific time (eg. vehicle or rocket control, or PLC systems you mention, etc) and "soft real time" meaning the response should be quick but nothing catastrophic will happen if it doesn't. Voice, video, and even text chat, falls into this category. You want minimal layency but nobody will die if the screen freezes for a bit. It's customary to talk about these systems as "real-time communication" and nobody working in the field would confuse it with hard real-time. More info and examples: https://en.m.wikipedia.org/wiki/Real-time_communication https://en.m.wikipedia.org/wiki/Real-time_communication