[houseofshards]

What does the article mean by "fast" radio signals ? Don't radio waves always travel at the speed of light ?

[JonathonW]

They're "fast" in that they only last a short period of time-- these signals only last a few milliseconds, and they're rarely detected in real-time.

[justinpombrio]

So... brief.

[gre]

They mean the signals last about a millisecond.