There is a difference, but most people won’t know about it, because they use their Apple ID as iCloud ID as well.
The Apple ID is used for apps, music, movies, books, ... Nothing else.
The iCloud ID provides all the services that come with iCloud: iCloud Photo Library and Photo Sharing, Find my iPhone, backups, storage space, ...
It’s possible to use your ID for App Store & iTunes Store, but not for iCloud. Some people use one ID for iCloud, and a different one for App Store, iTunes Store, iBooks Store. I was one of them, so I know that it’s possible.
That’s why I’m using both expressions differently.
The Apple ID is used for apps, music, movies, books, ... Nothing else.
The iCloud ID provides all the services that come with iCloud: iCloud Photo Library and Photo Sharing, Find my iPhone, backups, storage space, ...
It’s possible to use your ID for App Store & iTunes Store, but not for iCloud. Some people use one ID for iCloud, and a different one for App Store, iTunes Store, iBooks Store. I was one of them, so I know that it’s possible.
That’s why I’m using both expressions differently.