Alias is a command that lets you create command aliases, it is very useful when you usually use commands with options.

As an example in my case I use a lot these commands

du -h

and

df -h

In both cases the "-h" option makes the output be in Kbytes or Mbytes instead of bytes, so it is more human redeable.

To create aliases for this commands just need to enter.

alias du='du -h'

and

alias df='df -h'

Now both du and df will be executed with its -h option.

If you need to de-alias the command just enter:

unalias du

And the alias for du will be deleted.

To view a list of all aliases just type alias with no arguments on the command line.