What is a stored procedure?

CREATE PROCEDURE GetAllEmployees() BEGIN SELECT * FROM employees; END;

What does this do?

CREATE PROCEDURE GetEmpByDept(IN dept_id INT) BEGIN SELECT * FROM employees WHERE department_id = dept_id; END;

What is dept_id?

CREATE PROCEDURE GetEmpCount(OUT total INT) BEGIN SELECT COUNT(*) INTO total FROM employees; END;

What does OUT do?

How do you execute a stored procedure?