While I agree with your general premise, I disagree about the "not necessarily" part: whenever "relevant ad" is mentioned, it's pretty much always in the contex

While I agree with your general premise, I disagree about the "not necessarily" part: whenever "relevant ad" is mentioned, it's pretty much always in the context of "ad relevant to the viewer" (they just don't say it like that), instead of what "relevant" should really mean (relevant to the content being viewed, as you indicated). Let's take FB for example, under the hypothetical situation where they're showing what they would call a "relevant ad": A single mother, that has 2 kids, often talks/chats with other mothers about daycare, school activities, knitting, etc. One day out of the blue, she visits a FB group dedicated to electronics (say, assembling electronics, etc.). I can guarantee you that the first "relevant ad" she'd see on that group would NOT be about electronics, but rather something related to her interests, as tracked from her previous behaviours. If it were truly a "relevant ad", it'd be something about electronics, and everyone else that visited that group for the first time would also see this same ad, regardless of their past behaviour (much like your podcast ad example). Calling it "relevant ad" just means "ad relevant to the viewer", which simply translates to "targeted ad".