SEND stands for Special Educational Needs and Disabilities. The Code of Practice states that:
A child or young person has SEND if they have a learning difficulty or disability, which calls for special educational provision to be made for him or her.
A child of compulsory school age or a young person has a learning difficulty or disability if he or she:
has a significantly greater difficulty in learning than the majority of others of the same age
has a disability which prevents or hinders him or her from making use of facilities of a kind generally provided for others of the same age in mainstream schools or mainstream post-16 institutions
If your child is registered as having SEN this does not mean that they are not academically able. There are a range of SENDs that can be supported in different ways in school.