The same thing: a filter that only lets through low frequencies. A blur effect is a spatial low-pass filter. A motion blur effect is a temporal low-pass filter.

What GP is talking about is the antialiasing low-pass filter used when downsampling video to smaller resolutions, or when initially sampling it at the sensor. This is the same exact concept as the antialiasing low-pass filter used when downsampling audio to lower sample rates, or when initially sampling it at the ADC.

Perfect. Thanks!

Downscaling or blurring - these are the same thing if you pretend it’s bandlimited. Which it isn’t of course.

The signal is typically bandlimited by hardware — the optics and sensor. When it's not, you get weird effects, though that's rare because cameras have optical low pass filters to avoid this.

When they don't, like the Canon 5D mark ii when used in video mode (which just threw out most of the sensor's pixels to get to 1080p), you get aliasing producing moire patterns like this:

https://youtu.be/dMHDB5fG6ys?t=218