Aliases can be global, i.e. apply by default to every user on the system.
However each user can also have their own aliases which only apply to them, i.e. local aliases.
Global aliases are specified in a file within the /etc/profile.d/ directory. The name of the file is irrelevant.
We use /etc/profile.d/bash_aliases.sh.
NOTE: The permissions of the file should have read permissions.
For example 644.
Local aliases are specific to the user.
These aliases should be defined in a file named .bash_aliases within a users home directory.
To apply the changes immediately to your bash profile without having to log out:
source ~/.bashrc
or
~/.bash_aliases
or
. ~/.bashrc
or
. ~/.bash_profile