Agile is a mindset, not a process or methodology.
These practical resources can help you explain this to people.
What Is Agile?
Five slides to help you explain Agile to people.
Pair this video with the above slides to explain what Agile is.
Agile Is a Mindset
This image, created by ICAgile, simply and elegantly defines Agile.
The Benefits of Agile
This short animated video explains the Agile mindset.