What is the difference between Functional Requirement and Non – Functional Requirement?

The Functional Requirement specifies how the system or application SHOULD DO where in Non – Functional Requirement it specifies how the system or application SHOULD BE.

Some Functional Requirements are,
Authentication
Business Rules
Historical Data
Legal and Regulatory Requirements
External Interfaces

Some Non Functional Requirements are,
Performance
Reliability
Security
Recovery
Data Integrity
Usability