My iCloud password is different from my apple account password

Is there a functional difference between the websites iCloud.com & idmsa.apple.com? In my password list, I have the same email ID for both, but different passwords. I changed the idmsa.apple.com password 8 months ago, but the iCloud.com password is almost 3 years old & not as secure. On my iPhone 13, under sign-on & security, there is a place to change a password. I'm not sure which one I'll be trying to change or how to do it. I have iCloud + account.