In a DBMS Lab, `patient_id` is an important field used to identify a particular patient in a database table. When `patient_id` is defined as a Foreign Key, it establishes a relationship between two tables. A foreign key is a column or a set of columns in one table that refers to the Primary Key of another table. It helps maintain referential integrity and ensures that relationships between records remain valid. For example, consider a hospital database containing two tables: `patient` and `appointment`. The `patient` table may contain `patient_id` as its primary key. The `appointment` table can contain `patient_id` as a foreign key to identify which patient has a particular appointment. A simple structure can be represented as: ```sql CREATE TABLE patient ( patient_id INT PRIMARY KEY AUTO_INCREMENT, patient_name VARCHAR(100), age INT, gender VARCHAR(10) ); ``` The appointment table can then use `patient_id`