I define "tell" as summarizing, and "show" as going into enough detail that the reader experiences the story right along with the characters.

When you tell a friend about something that's happened, you don't give them a minute-by-minute, blow-by-blow description of the incident, unless every little detail is crucial. Instead, you summarize, so they get the idea/message/point.

How much detail and how many words you use in your writing are signals to the reader about how important something is in the story. If you gloss over it (summarize or "tell"), you indicate that it isn't as important as something you describe ("show") in loving detail.

When writers are urged to "show, don't tell," I submit that their readers or critiquers are actually saying, "spend more words on the important parts, or the parts you have led me to believe are important--don't summarize them, give me more details."

"Show, don't tell" could be a way of saying, "I don't think you have written enough about the parts that interest me, that I care about."