Many-to-Many (M:N) Relationship:
Example:
-Table "Students" and Table "Subjects"
-One student can enroll in many subjects (Many students to many subjects)
-One subject can have many students enrolled (Many subjects to many students)

One-to-Many (1:N) Relationship:
Example:
-Table "Students" and Table "Localities"
-One locality can have many students (One locality to many students)
-One student belongs to only one locality (Many students to one locality)

One-to-One (1:1) Relationship:
Example:
-Table "Students" and Table "Identity"
-One student has one identity (One student to one identity)
-One identity is associated with only one student (One identity to one student)