https://en.wikipedia.org/wiki/Fan_service
That's the Japanese take on it, which expands the concept further. That said, I think Reyna did a good job explaining it. Pokemon fanservice, so far, would be the recent appearances like Lucian or his explaining the Elite Four, which is something Western fans would obviously want. It's addressing the story more, like, say, Galactic's cameo, which writing-wise would be "ZOMG!!! SQUEE!"
Think on that compared to even a few years ago, "would the Japanese producers bother with such things?" Given the original treatment of the Elite Four, for example, I'm thinking no.
Then, of course, we have had Jessie's skirt shots and cleavage in the past, so that would be the intended Eastern fan-service. I guess we'll have to settle with Hikari's maid get-up, as standards have changed. I blame Dogasu, he started this trend. Or did I do it? Huh. I dunno.
Anyway, does that clear up things?