What is an Apple Push Notification service?

Hi I've been receiving emails from Apple which look legit but don't make any sense. They say "The following Apple Push Notification Service certificates, created for AppleID [my ID] will expire on May 18, 2017. You can renew your certificates with your Mac server administration tools"

What is this? I don't have a Mac. I have a PC and Laptop with Windows and an iPhone. I do have an iCloud account - is that what they are referring to - and does this message mean anything I need to attend to?

Ignore

"What is an Apple Push Notification service? *You can renew your certificates with your Mac server administration tools* I don't have a Mac. I have… An iPhone."

Apple recently decided that "Mac server" is not just for Mac. It can be used on iPhone or iPad. This can allow application development and upload via mobile phone service. Nowadays people want to be able to do everything mobile, without any Wi-Fi connection. You can read about it at the link below.