Serverless
Serverless means your code runs only when needed, on machines you never see or manage.
In a simple example
A contact form sends a message. A small piece of code wakes up, saves it, and goes back to sleep.
Why it matters to you
You pay little when few people use it, and it still copes when many come at once.
Do not confuse with
Serverless does not mean there are no servers. It means someone else looks after them.