Inference is the moment the system answers. Training is the practice. Inference is the live use: a customer asks a question, a photo is checked, a ticket is summarized. That is the step you pay for every time, and it is the step a user waits on.
When you plan a project, split the money in two. One amount to build it. Another amount, every month, to run it. A demo on a quiet afternoon does not show the bill of a busy Monday. Ask how many requests you expect, how long each answer may be, and what happens when a campaign doubles the volume.
Think of it this way: Training is learning to drive. Inference is every trip you take after passing the test. The exam happens once; the road charges you per mile.
A support team runs every inbound message through a model so it can sort what the customer wants. The build was a one-time project. The bill arrives again every month, and it grows with the number of messages.
An insurer adds a what does my policy cover box to the customer app. In the pilot, fifty people a day try it and the bill is small. After the email launch, four thousand people try it the same morning. The feature still works. The monthly run cost is now the larger line.
Inference is always involved when users interact with an AI feature. The question is whether you have designed for the running cost from day one. You cannot avoid inference if you want a live AI feature. But you can cut cost by caching frequent answers, shrinking prompts, and routing simple tasks to smaller, cheaper models. A recurring cost per use, not a one-time build cost.
You do not need to pick a model from this page. RaftLabs starts from the job: the documents, the decision, and what a wrong answer costs. You see a working version before a large build. The related work on our side is MLOps.
This sits with the other foundations terms on the glossary. The words under every AI conversation, from the model itself to the data it learned from. Worth reading next: Artificial Intelligence (AI), Machine Learning (ML), and Large Language Model (LLM).