Is Dyslexia a real thing? How can you tell? What is dyslexia?

I recently found a very helpful resource for children and adults with dyslexia, and their families and teachers. 

Headstrong Nation, at http://headstrongnation.org/, is a non-profit dedicated to serving the dyslexic community. 

From the site: 

"Founded by Ben Foss in 2003, Headstrong Nation aims to end the isolation of the world’s largest (it’s true!) disability group by providing information about dyslexia, self-advocacy and new technologies. To do this we help dyslexic adults and parents of dyslexic children learn the facts, figure out how to play to their strengths and connect with others to form a movement dedicated to leveling the playing field for people like us."