Nonfunctional requirements means requirements that are not directly related to functions of the system.

Examples are How will website behaves if 10000 users at the same time. What is the esponse time of home page at the same time.

How reliable is website.

How secure is it’s my password

How much usable an application is i.e. can we access the application in all browsers etc.

Other examples are Instaleabilty, maintainability, portability, recovery, reliability, usability etc.