Linux Shell (. /path/filename)

In the/etc/profile file, there is a script:

if  Then /etc/bash.bashrcfi      

What does "dot + space + file" mean here?

1, if we want to execute a file, but this file is not executable, at this time we want to use chmod u+x file_name to make the file with executable permissions
2, but sometimes we do not want to change the execution of this file permissions, but also want to execute this file, you can use (dot-space-file name) Form to execute a script (only the root user can do so)

Linux Shell (. /path/filename)