In this context, it just means "underappreciated" or "less widely known or acknowledged than other inventions of similar magnitude of impact". I don't think it

In this context, it just means "underappreciated" or "less widely known or acknowledged than other inventions of similar magnitude of impact". I don't think it's millennial slang; I'm almost 50 and I've heard it used this way all my life. However, I was vaguely aware that it had some original, more technical meaning, specific to some discipline like composing music or something like that. My interest in investigating was limited, though, so I only asked GPT-4o, who claimed: > Originally, the term "low-key" was used in reference to a lighting technique in photography and cinematography. It described a style that utilized less lighting to create a mood of intimacy, mystery, or dramatic contrast. This usage emphasized the subtle, understated nature of the lighting, which is less intense and less prominent than high-key lighting. Over time, "low-key" evolved to take on broader meanings, including understated, subdued, or not seeking attention, before arriving at its contemporary connotation of something or someone being low-profile or modest. (I'll accept that, I guess, unless disputed/refuted here by the actually sentient.)