# What is RLHF? Definition & Technical Mechanics

> **Source:** [SPIDITS AI AI Glossary](https://spidits.com/ai-glossary)  
> **Category:** Model Training  
> **Canonical Citation:** [https://spidits.com/ai-glossary/rlhf](https://spidits.com/ai-glossary/rlhf)

## Definition
Reinforcement Learning from Human Feedback (RLHF) is a training methodology used to align LLMs with human values and preferences. It uses human evaluations to train a reward model, which then guides the LLM to generate helpful, harmless, and honest outputs.

## Architectural Mechanics & Deep Dive
Reinforcement Learning from Human Feedback is the foundational alignment method that made models like ChatGPT conversational and safe. The process is divided into three key phases. First, Supervised Fine-Tuning (SFT) is performed on high-quality demonstration data. Second, human annotators rank multiple model outputs for quality, helpfulness, and safety; this preference data is used to train a separate 'Reward Model' that acts as a proxy for human judgment. Third, the policy model is optimized using Reinforcement Learning (typically PPO) to maximize the scores given by the reward model, keeping outputs aligned with human safety rules.

## Industry Applications & Real-World Use Cases
Model alignment, safety constraint training, and conversational tuning

## Frequently Asked Questions

### Why was RLHF used for ChatGPT?
Raw pre-trained models generate text based on next-word probability, which often leads to offensive or unhelpful text. RLHF aligns the model to act as a conversational assistant.

### What is a Reward Model in RLHF?
A secondary network trained on human preferences that scores model responses. This score is used as a reward signal in reinforcement learning.

## Related Terminology
- [reinforcement-learning](https://spidits.com/ai-glossary/reinforcement-learning)
- [llm](https://spidits.com/ai-glossary/llm)
- [fine-tuning](https://spidits.com/ai-glossary/fine-tuning)

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*From the SPIDITS AI Knowledge Base (336+ terms indexed). Explore full technical definitions: [https://spidits.com/ai-glossary](https://spidits.com/ai-glossary)*