Lo-fi (also typeset as lofi or low-fi; short for low fidelity) is a music or production quality in which elements usually regarded as imperfections in the context of a recording or performance are present, sometimes as a deliberate choice. The standards of sound quality (fidelity) and music production have evolved over the decades, meaning that some older examples of lo-fi may not have been originally recognized as such. Lo-fi began to be recognized as a style of popular music in the 1990s, when it became alternately referred to as DIY music (from "do it yourself"). Some subsets of lo-fi music have become popular for their perceived nostalgic and/or relaxing qualities, which originate from the imperfections that define the genre.

Traditionally, lo-fi has been characterized by the inclusion of elements normally viewed as undesirable in professional contexts, such as misplayed notes, environmental interference, or phonographic imperfections (degraded audio signals, tape hiss, and so on). Pioneering, influential, or otherwise significant artists include the Beach Boys (Smiley Smile and Wild Honey), R. Stevie Moore (often called "the godfather of home recording"), Paul McCartney (McCartney), Todd Rundgren, Peter Ivers, Jandek, Daniel Johnston, Guided by Voices, Sebadoh, Beck, Pavement, and Ariel Pink.

Although "lo-fi" has been in the cultural lexicon for approximately as long as "high fidelity", WFMU disc jockey William Berger is usually credited with popularizing the term in 1986. At various points since the 1980s, "lo-fi" has been connected with cassette culture, the DIY ethos of punk, primitivism, outsider music, authenticity, slacker/Generation X stereotypes, and cultural nostalgia. The notion of "bedroom" musicians expanded following the rise of modern digital audio workstations, leading to the invention of the nearly synonymous term bedroom pop. In the late 2000s, lo-fi aesthetics served as the basis of the chillwave and hypnagogic pop music genres.