Sorry for the shorthand.
A NAS is a network attached storage in other words a set of external hard disk drives and an computer controller wired to ones router ( usually )
They are typically used to provide local file storage for ones computers, backups and also they are often used to store music and video files that can be accessed on a computer, laptop and smart TV.
They are not cheap - maybe £300-450 for a two disc unit and, to be honest, I only have one because of the business I run or ran from home.
They do seem popular for general home use these days - often by photographers - and so I mentioned this option in case you had one where it becomes a fairly simple and cheap way to record camera footage.
Definitely not necessary though - cloud storage and traditional surveillance video recorders etc. will do the job.
My fault entirely, I'm a bit useless at techie stuff so I get easily confused. Thank you for your clarification