Open-weight model
An open-weight model is one whose trained parameters are published, so anyone can download, run and adapt it on their own hardware. Some are fully open source with training code and data; many share the weights only, under licences that may limit use.
In one line, for a 12-year-old
An open-weight model is an AI you're allowed to download and run on your own computer.
An example
Families such as Llama, Mistral, Gemma and Qwen publish open-weight versions that hobbyists and companies run privately.
Why it matters to people
Open models let schools, hospitals and governments keep data in-house and avoid lock-in. They also make safeguards easier to remove, so the debate over openness is about real trade-offs.