Open source (published source code)
Japanese オープンソース
Open source software publishes its source code, the program's blueprint, and lets anyone use, change, and share it again. Being able to see the code is not enough, so check the license.
Open source is like a cook publishing a recipe and saying you may cook it, change it, and share it with others. It is not only about being able to see the source code, the program's blueprint; anyone must be allowed to use it, in any field. The definition for AI goes further and asks for information about the training data, the code, and the weights to be released. A model that releases only its weights is called open weights instead.
Watch out Something introduced as open source can still come with usage limits. Meta's Llama is one example: the OSI does not accept its license as open source. Real open source has conditions too. The MIT License says the copyright notice and permission notice must stay in copies. Before you reuse code or a model, read the license name and its conditions.
Source: The Open Source Definition · The Open Source AI Definition – 1.0 · The MIT License · The Open Source Definition (v1.9), annotated Japanese translation (checked 2026-10-26)