For a long time, I hated this discussion, and I think I have an idea why now. Nobody is talking about the same thing here. It's like the Tower of Babel; we're all speaking different languages. I recently watched a few of these discussions unfold almost simultaneously online. As the discussions progressed, I became aware that everyone, even those who sounded wise and experienced, meant slightly different things when they used the words show and tell.
And here's my conclusion: you don't even need those words to discuss the topic.
Or, if you want me to be more blunt, it's a lot of bullshit.
The first thing I see, is that when writers hear that they need to show more and tell less, what it really means is that they aren't evoking emotion. The reader isn't feeling anything; they're merely being informed about what is going on in the character's heart and mind. This is true whether we're talking about action, thought, summary or dialogue.
And it doesn't matter if the line is, "Clair looked hurt," or "Clair wept," or "Clair's heart broke" or "Clair buried her face in her pillow and sobbed for hour".
What matters isn't how it is done so much as whether it evokes emotion. Many writers advise getting into the character's head with a deep narrative voice and working through the actual thoughts. I agree that it is often the best way, but not the only way.
The how-it's-done part comes down to four basic modes (though you could expand them if you wanted).
Writer of speculative fiction. Current work in progress is an untitled dark fantasy novella.