Figure 11-4
This illustration shows that four threads of the application connects to the database through a connection pool. The connection pool has two physical connections to the database which are shared by all threads. Each connection from the threads to the database can be considered as virtual connection.

T1, T2, T3, and T4 are four threads of the application.

TC1, TC2, TC3, TC4 are virtual connections from threads T1, T2, T3 and T4 respectively.

C1 and C2 are physical connections to the database.