The back quotes in Unix

I was trying out this great script to make backups:

http://nicaw.wordpress.com/2013/04/18/bash-backup-rotation-script/ thanks to Julius’ blog

I realised that there was a line:

date_daily=`date +"%d-%m-%Y"`

with the back quote `

Ok. I thought it could have been a problem of cut&paste because I have not come across this quote in other programming languages I use (ruby, javascript, php). But after a quick search I learnt that it is used to execute commands.

I learnt it here: http://www.tutorialspoint.com/unix/unix-quoting-mechanisms.htm