A Primary Key is a unique identifier for a record in a database table. It ensures that each entry can be distinguished from others, preventing duplicate records. For example, in a table of students, the student ID can serve as a primary key, as each student has a different ID number. Using a primary key is essential for maintaining data integrity. It allows for efficient data retrieval and relationships between tables. For instance, if you have a table of courses, you can link it to the students table using the primary key, making it easy to see which students are enrolled in which courses.