Silent means that it has no sound, but "sound" either means the sensation of perceiving vibrations, or the actual vibrations that cause the sensation. 0 dB SPL is the threshold of hearing, so it is "silent" in the first sense.

Strictly speaking.

He’s using the term incorrectly to begin with so corrections aren’t really possible.

Of course it can’t be completely silent. Heat generates air movement which is “sound”.

By 0dB he means 0dB SPL which is give or take correct.

If the air moves at a constant speed I don't think you'd get sound. Any fluctuations probably won't be in the audible spectrum, although whether that still counts as 'silent' is more of a philosophical question.

Yep. 0dB is the limit of human hearing, not absolute silence. There are anechoic chambers with noise levels below 0dB.

Yet if you sit in one you hear the blood pumping through your ears so it's reasonable to use human perception as a baseline when that's what they care about.

I've been in one. Back in HS, we took a trip to the GIANT anechoic chamber at Georgia Tech. It was incredible. If someone was facing away from you and yelling as loud as they could, you could barely hear it from behind them. You're standing on basically a giant net on top of a pit of foam blocks, and every wall is wildly shaped undulating foam.

It's really surreal and a number of people actually became nauseated at the sensation.

Pretty sure there's going to be some coil whine. Probably above 0dB.

I'm pretty sure that there's some measurable amount of coil whine or other noise coming from capacitors and other small components, making it more than -infinity dB, and probably more than 0dB. The sound might not even be within human detectable frequencies.

To be more pedantic, it's probably safe to assume this is not even 0dB. Most people would probably consider a computer under 25dB-30dB as "silent" since most rooms background noise are around there.

Linus did a silent PC build which even in a sound proofed case and at idle was about 14dB and broke 20dB under load: https://www.youtube.com/watch?v=RXZrWqCT7R0

Even the high end microphone used to record the sound level in this video produced it's own 7dB of noise.

It may register below 0dB SPL (in an anechoic chamber, anyway) depending on the manner in which it's measured, which is a complex discipline in itself. Sound pressure dissipates over distance, for example, so the distance at which the measurement is made has bearing, as does the angle at which it's measured.

(This is unabashed pedantry. But I'm on my lunch break, so...)

20 to 30dBA is probably the base noise level of most environments.

No point in making your PC less noisy than the noise floor.

Also, coil whine and convection wind have potential to be more obvious once you take away fans and introduce more efficient passive components.

I was just going to post this with a nitpicking warning. Anyway, it may be a joke.