Let's start by saying what it's not - it's not low intelligence, stupidity or laziness. And it's not the result of cultural differences, economic disadvantage or environmental influences.
It is a specific problem in the brain that affects the way a person processes and responds to information.
For instance, a child who is bright, active and of normal intelligence, may be able to tell a story, but may not be able to read or perhaps, write it down in any legible form.
ADHD occurs in people of normal intelligence, yet their ability to concentrate and control their behavior is limited.
Learning disability is not a disorder in itself - it is a term used to describe a range of disorders that affect a person's abilities in reading, writing, math, listening and speaking.
A learning disability is like an island of inability - it's just one part that's not working right or needs a different kind of attention.