As mentioned, most can be used as an intensifier ( ≈ "very" "quite" "exceptionally") IF it is preceded by something other than the. It is much more often used as a superlative when preceded by the. (the [only] most ... because there can be only one).
The intensifier "a most pleasant" is considered very formal, as "ever so much", mentioned above.
However, there's an exception to this rule: "the most..." is used as a highly informal intensifier, and is considered "Valley Speech"-type slang. Often used in reverse fashion along with "literally" used to mean not literally. This could be considered a mistaken use of both words, or as ironic slang (dialect, not ungrammatical — especially if no "literal" superlative could possibly exist). But it's the opposite of the formal usage mentioned above. And hence you're more likely to encounter it as an intensifier in slang form, with heavy emphasis placed on "the most" to indicate sarcasm. But it's the most likely context you'll see for the most as referring to anything other than the most.
"He was the most stellar singer I've ever heard."
— "the most ... (ever)" is standard and always indicates superlative (the single most)
"[Like, ...] he was literally the most annoyingly sympathetic person."
— Highly informal and possibly sarcastic. Note the lack of any possible literal superlative, so this is dialect, not grammar, but still, only in an informal setting. "valley speak intensifier"
"The scene outside the Opera was most upsetting. I almost dropped my monocle. Thank you ever so much for retrieving it."
— Highly formal, rarely used outside of formal situations
"The scene outside the Opera was the most upsetting. I demand to be taken back to the Embassy now!"
— Borderline case. When used as a superlative (the...), it must always refer to the (single) most of anything. It may be used as deliberate bad grammar in fiction to indicate a non-native English speaker, as (obnoxiously) in "The Very Best Exotic Marigold Hotel".
Then again, "the very best" can also be used as a slang intensifier, like "literally", "definitely", and "the most", to mean something other than the absolute best. But "the very best" has more wide acceptance in this phrase. When paired with a class description, "the most" and "very …est" are always definite superlatives.
You'll sometimes see formal or informal use of other …est as an intensifier as well, always without a class description to indicate the superlative. ("we had the happiest time!" is usually informal or polite; not as strong a statement as "we had the happiest vacation in 5 years" which is a more formal statement of fact).
Note that the emphasis is always placed on the "…est" when using it as an informal intensifier. "It is simply the most gracious gift!" (The most of what? nothing — It's an intensifier, as the emphasis indicates.) "It is the most gracious gift…" suggests an incomplete thought; perhaps the speaker forgot to get you something. ;-)