From Longman Dictionary of Contemporary Englishuser nameˈuser name, username /ˈjuːzəneɪm/ ●●○ (also user ID) noun [countable] a name or special word that proves who you are and allows you to enter a computer system or use the Internet Please enter your user name and password and click ‘OK’.
Examples from the Corpus
user name• You gain access to your data by typing in a user name and password.• Note that on all subsequent pages, the supplied user name will be displayed at the top of the page.• The user name can be up to 28 alphanumeric characters long including spaces.From Longman Business Dictionaryuser nameˈuser ˌname (also username also user ID) noun [countable] computing a name that proves who you are and that you must type in before you can enter a computer system, use a program etcPlease enter your user name and password. 