What is web app? Is it a software? What knowledge and skill is required to make an web app?
Have you done any research on your question? You might try typing "what is a web app" into a search engine, and see what you get.
HAHAHAHA, you're so right about that! I'm sorry that I was clueless.
Based on another question you asked here recently, you might be especially interested in one of those search results, the one on Stack Overflow with the title What's the difference between a web site and a web application?
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