The story
From mix + tape; originally mix tape. Originally referring to a homemade compilation recorded onto a cassette tape and circulated informally, especially within hip-hop culture, mixtape has broadened in sense. In contemporary usage it often denotes a musical project released outside the conventional album framework, typically characterized by looser structure, experimental material, or informal distribution, even when no physical tape medium is involved.
Etymology from Wiktionary, CC BY-SA 4.0.