Machine learning
Machine learning is the main way modern AI is built: instead of writing every rule by hand, developers show a program many examples and let it adjust itself until its outputs match. The result is a model that can handle new cases it has not seen before.
In one line, for a 12-year-old
Machine learning is teaching a computer with examples instead of instructions, like learning to ride a bike by practising, not by reading a manual.
An example
An email service learns to recognise spam after seeing millions of messages people marked as junk.
Why it matters to people
A system that learns from examples also learns their gaps and prejudices. Who chose the examples, and who checked them, shapes how fairly it treats people.