That’s what you have if you mechanically keep the shutter open for a prolonged time, exposing either film or a sensor to light.

But from what dang was saying, he seemed to describe emulating that effect in software on discretely captured frames.

Sounds almost closer to onion skinning, and in particular the part of this article https://en.wikipedia.org/wiki/Onion_skinning where they say:

> This effect can also be used to create motion blurs, as seen in The Matrix when characters dodge bullets.