Dyscalculia is a specific learning disability which affects math. It is often called "math dyslexia". It is similar to dyslexia but is less well known and therefor diagnosed less often.
Dyscalculia does not affect general intelligence. Children can be highly intelligent in other areas yet struggle with math. This often makes it perplexing for parents. They recognize the intelligence in their children yet don't understand why their child struggles in math. It can often be misinterpretted as laziness.
DSM-5 Definition
In the DSM-5 (Diagnostic and Statistical Manual of Mental Disorders) the use of the word dyscalculia is no longer reccomended
The DSM-5 now reccomends use of the phrase "Specific Learning Disability" to replace the previously used dyslexia (reading),dyscalculia (math), and dysgraphia (writing). The definition as given by the current version of the DSM-5 is:
A neurodevelopmental disorder of biological origin manifested in learning difficults and problems in acquiring academic skills markedly below age level and manifested in the early school years, lasting for at least 6 months; not attributed to intellectual disabilities, developmental disorders, or neurological or motor disorders
This definition is to then be used with clarifiers to define whether the condition affects reading, writing, or math.
Department Of Educations Skill (UK) defines it as such
Dyscalculia is a condition that affects the ability to acquire arithmetical skills. Dyscalculic learners may have difficulty understanding simple number concepts, lack an intuitive grasp of numbers, and have problems learning number facts and procedures. Even if they produce a correct answer or use a correct method, they may do so mechanically and without confidence
Definitions have purposes for clinicians and bureacracies but if you are a parent who just want to help their child this all may be quite useless unless you are seeking an official diagnosis. If you are just looking for information on how to figure out what is going on and how to help your child you might consider our dyscalculia screener. It will send you a detailed report with actionable answers.