How search works in iTunes with podcast keywords
Podcast title, summary, episode title and episode summary are key places for search terms.
Previously, keywords were utilized more than they are now. iTunes now focus on the title, author, and description tags.
From the official Apple iTunes documentation:
Pay close attention to the title, author, and description tags at the `<channel>` and `<item>` level of your podcast feed. The iTunes Store uses these fields for search. The metadata for your podcast, along with your cover art, is your product packaging and may affect whether your podcast shows up in relevant searches, and how likely users are to subscribe to it.
Keywords may be utilized in the future, but as Apple's documentation has noted, they focus on those fields for search and discovery (other RSS readers may use your keywords).