My Apple ID
appleid.apple.com
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
An Apple ID is your user name for everything you do with Apple: Shop the iTunes Store, enable iCloud on all your devices, buy from the Apple Online Store, make a reservation at an Apple Retail Store, access the Apple Support website, and more.