yes, 3 tier web application almost used everywhere

-- 3 tier web application almost used everywhere.
-- That's the reason why I teach 3 tier architecture in the first chapter.
-- Simply speaking the 3 tier includes: Web Server, Application Server, and Database Server.
-- The concept is not hard to learn.
-- As you said, people only learn from individual class may not get the concept of all the 3 tier together;
-- Company usually asks this question to test how deep you know about the concept of IT web based system.