I am a beginner in PHP and have recently come across some variables in my code that have underscores (_) in their names. I have seen variables like $first_name and $last_name, where the underscore separates multiple words. I am confused about the purpose and meaning of these underscores in PHP variables. Can someone please explain to me what underscores mean in PHP variables? Is it just a matter of personal style or is there a specific reason behind using underscores in variable names? Thank you in advance for your help!