The Open Source AI Definition (OSAID) is the first industry-standard definition of open source artificial intelligence published by the Open Source Initiative (OSI). It provides a standard through community-led open and public assessment to verify whether an AI system can be considered open source AI. The release of OSAID v1.0 is the result of many years of research and collaboration, following international symposiums and a year-long co-design process. This definition requires open source models to provide sufficient training data information so that skilled individuals can use the same or similar data to reconstruct a roughly equivalent system. The release of OSAID is significant in promoting openness, transparency, and collaboration in the AI field, emphasizing the core position of open source principles in AI development and supporting transparency between independent machine learning researchers and large AI developers.