An open-source (more precisely: open-weight) model publishes its trained parameters so anyone can download, run, inspect, and often modify them — instead of offering only hosted API access. Licenses vary widely in what they actually permit.
Open models shift power: they enable local running, customization, research scrutiny, and independence from a single provider — while raising their own misuse and support questions.
A company downloads an open-weight model and runs it on its own servers so sensitive data never leaves its infrastructure.