"Ambient Music," Brian Eno wrote, "must be able to accommodate many levels of listening attention without enforcing one in particular; it must be as ignorable as it is interesting." The line sat in a brief liner note on the back of an album he recorded in 1978, "Ambient 1: Music for Airports" — a note that has been cited more often than the music inside. The record came out the following year on E.G. Records (distributed by Polydor), the first in his Ambient series.

The definition was a deliberate reaction. Muzak (Muzak Holdings) had been selling bland, anonymous background music — the original "elevator music" — to stores and offices since the 1930s, and by the 1970s the company's own name, "muzak," had become a cultural slur for empty, deadening sound. Eno's claim was that there was a different way to make music for environments: music that treated the environment as compositional material rather than something to drown out. "Music for Airports" was reportedly played for a brief period at LaGuardia's Marine Air Terminal around 1980 — though accounts say travelers found it unsettling and it was pulled before long, and the details are disputed.

The piece is famous for its tape loops of different lengths, which drift in and out of phase with one another so that the same combination of notes recurs only every several minutes. The result is music that resists memorization, which is exactly the point — you cannot listen ahead, because there is no ahead.

Eno had been moving toward this idea for years. The 1975 album "Discreet Music" already fed a short, self-generating score through a tape-delay system (a setup that repeats sound at staggered intervals). "Music for Airports" formalized the project and gave it a name. From 1978 onward, "ambient" became a real category — a section in record stores, a label for the whole careers of the musicians who followed (Harold Budd, Laraaji, Jon Hassell). What it meant, however, started to drift almost immediately.

When Richard D. James, recording as Aphex Twin, released "Selected Ambient Works 85–92" on R&S Records' Apollo sublabel in 1992, the title was provocative. The album was a compilation of bedroom recordings made when James was roughly between thirteen and twenty-one (1985 to 1992), and most of the tracks had drum machines on them. Eno's definition specifically excluded music that enforced a particular listening attention; a drum-machine beat pattern forces exactly that kind of attention.

What James was doing was taking the textural and harmonic side of Eno's idea — slowly drifting pads, long evolving timbres, a deliberate refusal of pop song structure — and grafting it onto the rhythmic architecture of the early Detroit and Sheffield techno he had grown up listening to. The result was an album that did not fit any existing genre. The trade press initially called it "ambient techno." The looser label "intelligent dance music" came later: the name spread from a mailing list founded in 1993 (the so-called IDM list) — a label applied in retrospect, a year after the record it described. It was a deeply unfortunate term, condescending in its implication that other dance music was unintelligent, and disliked even by fans of the time, but one that stuck for a decade.

The 1994 follow-up, "Selected Ambient Works Volume II," mostly dropped the beats and moved closer to Eno territory, though darker and stranger. By then "ambient" as a marketing category had split into two streams. One was Eno-descended ambient, which kept trying to be the original definition's "music for environments" — best represented by William Basinski, the composer who made works out of decaying tape loops themselves. The other was beat-leaning ambient, which used the word "ambient" to mean "electronic music that is not for dancing" — music to cool down to after a rave, like the KLF's "Chill Out" from 1990. That is a different thing entirely. Throughout the 1990s, the chill-out room at major raves was where these two strands met and jostled for the same audience in the same space.

In February 2017, a YouTube channel called ChilledCow — later renamed Lofi Girl — began streaming a continuous loop of beats with the title "lofi hip hop radio — beats to relax/study to." The first stream used a clip from a Studio Ghibli film ("Whisper of the Heart"); it was removed for copyright reasons in July of that year, and in 2018 the channel relaunched the stream with the now-iconic original animation of a girl studying at a desk by a window. The audio was a rotating playlist of producer mixes built around slow, jazzy, deliberately roughened hip-hop instrumentals. The music descended directly from the work of two producers — J Dilla in Detroit in the early 2000s and Nujabes in Tokyo around the same time — who both built hip-hop tracks from sampled records. Dilla in particular all but invented the technique of chopping jazz records and leaving the wobble and grit in on purpose, and that touch was handed down intact.

By 2020 the stream had been running essentially continuously for three years and, across the pandemic months, peaked at tens of thousands of concurrent listeners and accumulated hundreds of millions of views in total. The genre it brought to wide attention — sometimes called lofi hip-hop, sometimes chillhop, sometimes just "study beats" — inherited the techniques hip-hop's instrumental tradition had built up: heavy, classic hip-hop drums known as boom-bap, jazz sampling, filters that shave off the high end, the crackle of a vinyl record. But it used the music in a way Eno would have recognized. The intended function was background. The user was a student or a remote worker. The track length and structure were designed to be completely ignorable over multi-hour sessions. The aesthetic of degradation — tape hiss, wow and flutter, the deliberately under-mastered mix — became a signal that this was not music demanding attention.

The word "ambient" was rarely applied to lofi hip-hop at the height of its visibility. It was filed under hip-hop, electronic, or background music. But functionally, in Eno's 1978 sense, it is ambient music: composed to accommodate many levels of attention, as ignorable as it is interesting, defined by its relationship to an environment (in this case, the home office or the study desk) rather than by its internal structure.

It is worth pulling the three uses of the word apart. Eno in 1978 used "ambient" prescriptively: this is the kind of music I want to make, and here is what it should do. The Aphex Twin and 1990s chill-out use was retrofitting: here is music already made that doesn't fit existing categories, and "ambient" is the nearest available shelf. The Lofi Girl use was functional and tacit: here is music designed for a specific behavioral context, and we will let listeners figure out what to call it.

This is a normal pattern for genre vocabulary. Words that begin as artistic manifestos drift into commercial categories and finally into descriptions of use. "Punk" did this in the late 1970s. "Indie" did it in the 1990s. "Lo-fi" itself did it twice — once in the 1990s American underground (Pavement, Sebadoh, Guided by Voices, all of whom were guitar bands playing live instruments and would have rejected the word "ambient") and once in the 2010s as a synonym for a beat aesthetic that has nothing to do with that scene.

What does survive across all three generations of "ambient," though, is the original argument. Eno claimed that the most interesting question about background music is not whether it is good or bad in isolation, but what relationship it sets up with the room and the listener's attention. "Music for Airports" answered that question for the airport. "Selected Ambient Works" answered it for the bedroom and the chill-out room. Lofi hip-hop radio answers it for the always-on browser tab. The musical materials change with each generation. The basic question stays the same: what is this music for, and how much attention does it ask of you?