Aliases in the cPanel content are referring to the mail aliases that you have created for your email. The mail aliases are an email forwarder that you setup for your domain, sub domain or your domain aliases.
For example: If you have an email forwarder which is forward from email@example.com to firstname.lastname@example.org, the backup aliases will help you to backup the setting of this forwarder.
Filtering is referring to your email filtering rules which you have created for your domain to filter the spam email. Backup filtering is used to backup all your email filtering settings so that you do not need to recreate the filtering rule again if you move from one server to the other. It is very useful when you have a lot of filtering rules for your email account.
The cPanel allow you to backup any selective domain, sub domain or domain aliases based on your needs. You may refer to the below picture on how to backup the mail aliases using backup aliases: