Axiom is a very very complex piece of software. It has code in several languages, implements languages, uses literate programming, it contains a very large library of mathematical concepts, documentation for those, tests, ...

So, it is not lines, but really a million things, functions, documentation snippets, tests, ...

That's also in line with my thinking. I'm not thinking in code lines, but live domain level objects.

Presumably he meant 'lines' of code but in lisp the concept of a single line of code is a little vague so he modified it to 'things'

Quite probably he meant S-expressions, but said 'things' to avoid scaring away those unfamiliar.