"application" user. If it is relevant to the domain, and there is nothing wrong with that. It's not vague. Next stupid post.

Travelers can view their booking through the website if they have the PNR locator. Purchasers can modify the booking through the website if they have the last 4 digits of the credit card number. Travel agents can see and modify bookings made through their agency. Airline check-in agents can see and modify bookings based on their role and airport, given identifying information from the traveler.

these are user roles. They may "inherit" from user for convenience, although inheritance should be avoided if possible, but are absolutely mixing up concerns here.

Now nothing prevents you from calling an object from the User class "traveler" locally, that's good practice. But to say "never use the word user in your code" is dumb.

Unix doesn’t have “users”

Unix absolutely has the concept of users. But it doesn't matter, your web application is not mimicking how Unix handles ACL to begin with so it's a silly argument.