This is one of these fun holidays celebrated on the First Thursday in May every year.
It was created to awareness of how important it is to take care of your passwords. In my experience, all data breaches, that I have seen and I have seen quite a lot has been caused by bad password security.
For example, we had someone who had their passwords on a sheet of paper that was stuck on the wall near the computer and anyone who came into the office could read it.
If you want to know some figures on what a data breach could cost you, click here.
Do not use the same passwords for all your sites.
Try and make each of your passwords as long and unique as possible.
If this is too hard, have you considered using a password manager? My favourite one is lastpass.