> Watching Star Trek TNG as a kid, I vividly recall hearing Geordi or Data often say things like "run a level 3 diagnostic on the Worf Barrels" or whatever to the computer and wonder what the heck that would even be....
reply> Now I think I kind of have an answer. Maybe the level of diagnostic refers to the LLM effort level....
The real answer is that it was gibberish. IIRC, the writers would insert "[tech]" in the scripts, to be later fleshed out into technobabble.
What you say is ret-con at best. A more realistic contemporary interpretation of the "level 3 diagnostic" technobabble, would have been a particular pre-programmed diagnostic procedure (like "run the POST memory checks" on a PC).