In England, the government defines special needs as:

A child has special educational needs if they have a learning problem or disability that make it more difficult for them to learn than most children their age. They may have problems with schoolwork, communication or behaviour.

'Special educational needs' is a legal definition and refers to children with learning problems or disabilities that make it harder for them to learn than most children the same age.

https://www.nidirect.gov.uk/articles/children-special-educational-needs

There are four main areas of Special Educational Need:

cognition and learning

communication and interaction

social emotional mental health

physical and sensory