What are SEO folks to do when a client you have been working with or four months asks ‘What is SEO anyway?’

No panic necessary. Take a deep breath, count to 10 and then baffle with jargon.

In a nutshell it is thus:

Create human-focused content that answers known queries and needs. (Consider meaning, medium, and message.)
Identify entities, attributes, and connections in content (through schema.org and other markup) for search engines to digest.

Ensure content is crawlable, indexable, and sharable.
Seek, enhance, and inspire authority signals via social, PR, and good old marketing!