The non-functional requirements of a software product are: 
reliability, usability, efficiency, delivery time, software 
development environment, security requirements, standards 
to be followed etc. 

Non functional requirements are those, which are not 
specified directly in the Requirements Document. But are 
implemented by the developers for foresaid reasons.

constraints on the services or functions offered by the 
system such as timing constraints, constraints on the 
development process, standards, etc.

stress testing,load testing,recovery testing,restart 
testing,security testing etc...

In general, functional requirements define what a system is supposed to do whereas non-functional requirements define how a system is supposed to be. Non-functional requirements are often called qualities of a system. Other terms for non-functional requirements are "constraints", "quality attributes", "quality goals" and "quality of service requirements". Qualities, that is, non-functional requirements, can be divided into two main categories:

Execution qualities, such as security and usability, which are observable at run time.

Evolution qualities, such as testability, maintainability, extensibility and scalability, which are embodied in the static structure of the software system.