AI, Physical AI, World Models, VLA, VLM, and Other Terms We Should Stop Mixing Together

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The robotics AI stack is becoming crowded with terms that are often used together, and sometimes used incorrectly.

Physical AI. World Models. World Foundation Models. VLMs. VLAs. Robot Foundation Models. Digital Twins. These terms are related, but they are not interchangeable.

For engineers, researchers, product managers, and founders working around robotics and autonomous systems, the distinction matters. It affects architecture, data collection, evaluation, safety claims, deployment risk, and product positioning.

This post is a practical glossary for the new Physical AI stack, an attempt to make the terminology sharper.