What is this spring.jpa.open-in-view=true property in Spring Boot?

I saw spring.jpa.open-in-view=true property in Spring Boot documentation for JPA configuration.

• Is the true default value for this property if it’s not provided at all?;
• What does this really do? I did not find any good explaining for it;
• Does it make you use SessionFactory instead of EntityManagerFactory? If yes, how can I tell it to allow me to use EntityManagerFactory instead?

Thanks!