What is candidate key with example?

A candidate key is a set of one or more attributes in a database table that can uniquely identify a record within that table. Each candidate key must satisfy two properties: uniqueness (no two rows can have the same value for the candidate key) and irreducibility (removing any attribute from the candidate key would make it unable to uniquely identify records). For example, in a table of employees, both the "Employee ID" and "Social Security Number" can serve as candidate keys, as each can uniquely identify an employee.