The ADDIE model is a systematic instructional design process consisting of 5 phases - Analyze, Design, Develop, Implement, and Evaluate. It was developed in 1975 and has become a standard for instructional designers. The 5 phases include analyzing learning needs, designing instruction, developing materials, implementing the instruction, and evaluating its effectiveness. The model provides a flexible framework for building effective training by identifying goals, creating content, testing, and assessing outcomes.