Open source
Software with source code publicly available + a license allowing inspection, modification, redistribution. Term coined 1998 by Christine Peterson as a more business-friendly alternative to "free software".
OSI (Open Source Initiative) formally defines: 10 criteria in the Open Source Definition. Major license families: permissive (MIT, BSD, Apache 2.0 — minimal restrictions), copyleft (GPL, AGPL — derivatives must also be open). Market evolution: from "anti-business" → trillion-dollar industry. Major moments: Linux (1991), Apache (1995), GitHub (2008), Microsoft acquires GitHub (2018), AI models' "open-weight" trend (2023+, Llama). Recent tension: "source-available" licenses (BSL, SSPL) — open source purists don't accept them.