In computing terms the difference between app and login

is that app is an application (program), especially a small one designed for a mobile device while login is the process of logging in.

As nouns the difference between app and login

is that app is abbreviation of lang=en while login is a combination of a user's identification and password used to enter a computer, program, network, etc.

As an initialism APP

is actinobacllus pleuropneumoniae.

As a verb login is

misspelling of lang=en.