Also known as itag or format codes and way back they could be specified with the fmt parameter (e.g. &fmt=22).
Depending on the age and/or popularity of the video, not all formats will be available.
AV1 HFR High
VP9.2 HDR HFR
HFR stands for "High Framerate", which means up to 60 FPS, whereas non-HFR is limited to 30 FPS
Non-HFR 1080p+ H.264 and VP9 variants are not provided for HFR videos anymore
Same IDs are reused for 360° videos
1440p+ H.264 variants are only provided for 360° videos anymore
At the moment, AV1 variants are only provided for popular videos
All AV1 variants can be HDR (no separate non-HDR AV1 variants are offered)
AV1 HFR High: High refers to the bitrate. These variants have ~3-4 times the bitrate of their normal counterparts. Additional side effect is providing AV1 HFR variants for low resolutions (<=480p). These variants are rare even among videos with AV1 variants. Found on this video.
AV1 HFR 4320p: Format 571 has roughly 50% higher bitrate than 402. Sometimes only one of them is offered, sometimes both. Can be seen on this video.
AAC (HE v1)
Rarely, YT Music
Yes, YT Music
No, YT Music*
(VBR) ~50 Kbps
(VBR) ~70 Kbps
(VBR) <=160 Kbps
AAC (HE v1)
(VBR) ~480 Kbps (?)
Surround audio can be found on some demo videos
YT Music: These formats are offered on Youtube Music. Format 141 is only available to Premium users with High Quality option
Actually @pgorod, they did mean 432Hz. This isn't referring to a sample rate, but rather a tuning standard. Instruments are usually tuned using the note A4 as reference. Most of the time, A4 is considered to be 440Hz, but there are some who believe that everything sounds better when tuning A4 as 432Hz instead. You can read more about it here, if interested.
So this has nothing to do with audio quality or specs, and as such you don't find anything useful about it with
youtube-dl. It's not a claim for a superior experience in a technical sense, but rather a musical sense.