Thread: What are atoms?

Here is a question I was asked at a job interview not too long ago.

'Explain what atoms are in simple terms'

Despite a degree in physics, I made a dog's dinner of this & gave some rubbish about really really small things.

I was thinking about it recently and looked up a definition & found:

atom: the smallest particle of matter which can partake in chemical reactions.

Sounds straight forward. But then I thought, what is a chemical reaction? Isn't it just an interaction between atoms (and collections of atoms). But that's recursive isn't it?

Any suggestions for answers?