Imagine a Youtube video where the host takes a break to read off an advertisement and that you'll get a 10% discount if you use their code during the checkout process. And then they resume with their content.

They often will pre-record these segments with a consistent "now with a quick word about our sponsors" jingle which can be statically detected and removed from the video.

It means things like sponsor spots where the YouTuber starts talking about some random mobile game or VPN provider you can tell they don't really care about

They are sponsor segments like this: https://www.youtube.com/watch?v=a8apEJ5Zt2s&t=33s

Some YouTubers do ad reads during their videos from sponsors.

"This video is sponsored by X. Get N% off by going to example.com/mychannelname or use the code mychannelname at checkout."

Got it! Thank you all for clarification, my comment is irrelevant then.

it's the sort of thing that happens at 4:10 in this video: https://youtu.be/jxICCEoiq74?t=240