AI system: An AI system is a machine-based system that works with some autonomy and infers, from the input it receives, how to produce outputs such as predictions, content, recommendations or decisions. That is the AI Act's core definition, and everything else in the Act builds on it.
In plain words
If the software figures out the answer itself, it is probably an AI system. If a person wrote every rule it follows, it probably is not. A chatbot that answers in its own words is an AI system; a menu of fixed buttons is not.
What it means for a small business
Most AI tools a small business uses are AI systems: website chatbots, AI image makers, AI writing tools and AI email assistants. Using one in your work makes you a deployer, with the transparency duties that come with it.
Example
ExampleA bakery's website chat that answers questions about orders by generating replies with an AI model is an AI system. A contact form that emails the owner is not.
Source
Regulation (EU) 2024/1689, the AI Act, Article 3(1), on EUR-Lex. This page explains the term in plain words; it is not legal advice.