A type of non-lyrical* music that contains origins and influences from Boom-Bap/ New York Underground instrumentals, 1960's and 1070's jazz samples, and electronic music. It's name, Lo-Fi comes from the term "low-Fidelity" which in this case if reference to the sounds of vinyl crackle and sample distortion which is used in a number of ways, namely the provocation of nostalgia, and to distance the sample or melody from any other song with a similar sound. Lo-Fi is primarily composed of a beat (similar to that of a hip-hop beat but with less bass) and looped samples (commonly used samples include piano melodies and clips of Wes Montgomery) most songs are relaxing and evoke positive emotions, often time nostalgia.

*there are occasionally samples of people's voices, usually from early television or radio recordings.

Person A : Dude I'm getting tired of all this high energy electronic music, I just want something jazzy to relax with
Person B : Have you tried listening to Lo-Fi, There's some really nice stuff out there. Start with the Tired Boy album by Joey Pecoraro.

Source: Urban Dictionary