When is /etc/bash.bashrc invoked?

From Debian's bash README:

5. What is /etc/bash.bashrc? It doesn't seem to be documented.

   The Debian version of bash is compiled with a special option (-DSYS_BASHRC) that makes bash read /etc/bash.bashrc before ~/.bashrc for interactive non-login shells. So, on Debian systems, /etc/bash.bashrc is to ~/.bashrc as /etc/profile is to ~/.bash_profile.

Technically, /etc/bash.bashrc is invoked for interactive, non-login bash shells for all users.

However, usually /etc/profile (which is invoked for all login shells) calls /etc/bash.bashrc as well. So that means /etc/bash.bashrc is also invoked for all logins shells as well.

However, the first line usually checks quits if non-interactive.

So in the end, effectively /etc/bash.bashrc is executed for all interactive bash shells (login and non-login). Think of it as the system-wide ~/.bashrc