This is the current legal definition.
Definition: A 'learning disability' is a disorder in one or more of the basic psychological processes involved in understanding and using language spoken or written which may manifest itself in an imperfect ability to listen, think, speak, read, spell, or do mathematical calculations.
LD (Learning Disability), and SLD (Specific Learning Disability) are the current terms for people who learn differently.
Dyslexia (reading disability), Dysgraphic (writing disability), and Dyscalculia (math disability) along with a lot of other "disabilities" are all considered a 'learning disability".
ADHD (attention deficit hyperactivity disorder) is not considered a learning disability.
This condition is also referred to as ADD and AD/HD. It is defined as inattention and heightened activity level. When learning is affected, they may also be said to have a learning disability.
Here are some sites with information on "learning Disabilities". As a person who had difficulty learning to read, with spelling, with math, with following verbal instructions, and remembering data, I strongly disagree with the negative attitude of most of these sites. This is because of my experience. I am myself a person with "learning disabilities", have raised a child with "learning disabilities", and successfully tutored children with "learning disabilities" for 40 years.
In high school, I was counseled that since I was incapable of handling college material, I should instead become a decorator. I flunked the ACT test in math and was told that I couldn't go to college. Since I had straight A's at my junior college, they decided to give me a try. Two years later, I graduated with honors from a prestigious private college with an Elementary Teaching Credential.
Since then, I have become a newspaper editor, business manager, magazine writer, technical writer, blog writer, creative writing teacher, and a very successful tutor for children who are struggling in school.
Have I been cured? Of course not! I am still me. I am still a very strong global learner (right-brained). I still have trouble with all the detailed left-brained activities such math, spelling, verbal instructions, phonetic reading, and reading out loud. I can help children with "learning disabilities" because most of them are also global learners (also called visual spatial learners).