This command, when invoked without arguments, shows the list of aliases in your shell session:
alias dir='ls -l'
alias l='ls -alF'
alias md='mkdir -p'
It also allows you to create your own aliases:
$>alias lc='ls --color'
If for some reason, you want to delete an alias, you can use the unalias command:
Aliases can help you saving a lot of time by avoiding repetitive and long commands and options.
If you want them to be permanent, you should add those definitions to your .bashrc file.