What is the definition of "special interest" and what does "special" refer to?

I understand that a special interest is a lot about something that a person is very good at but I could be wrong. The stereotype is a person memorizing lots of info, ie an interest in which you do not have to be good at something physical or motor skills.

Can a special interest be very physical?

I hear about how much enjoyment a special interest can give a person.

Does this mean that people with ASD are good at dealing with difficulties that they will experience when engaging in it?