Lenny’s Newsletter · Subscriber post · Building AI products · Communication & influence

An AI glossary

The most common AI terms explained, simply

Lenny RachitskyJun 24, 202514 min♥ 528
SourceLenny’s Newsletter
KindSubscriber post
PublishedJun 24, 2025
Readers♥ 528
Originallennysnewsletter.com ↗
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A glossary explaining 20+ common AI terms in simple language, from models and LLMs to transformers, training, RLHF, RAG, evals, agents, and hallucinations. It aims to help readers follow AI conversations in meetings and product work, framing jargon through plain analogies and linking to external primers.

Subscriber post — summary only

01Key takeaways

  • Most AI jargon maps onto a few core ideas: pre-training, fine-tuning, RLHF, prompt engineering, and retrieval at run-time.
  • RAG supplies current or task-specific context at inference time, which is a common way to reduce hallucinations.
  • Evals act like unit tests for AI products, defining what good output looks like and catching regressions.
  • Agents sit on a spectrum, becoming more agentic as they act proactively, plan, use real tools, and loop on their own output.
  • MCP is an emerging open standard that lets models connect to external tools without custom integration code for each one.

02Frameworks mentioned

Summary and takeaways written by PM Atlas; quotes are short excerpts. © the original author.