JPA relationships model the links between entities: @OneToMany, @ManyToOne, @OneToOne, and @ManyToMany. They translate into foreign keys or join tables, and can be unidirectional or bidirectional. The @ManyToOne side generally carries the foreign key.
Example
@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(name = "client_id")
Client client;