Web application is perhaps too loose of a term, but it's a start.
Let's break it down.
- HTML is data, CSS is presentation, and JavaScript is code. These are web technologies.
- These are usually brought together by a browser.
- Something in a browser on the web is a website.
- JavaScript suggests it is somewhat interactive, so it's not just a site, it's an application.
("Application" also suggests that it's more complex, like with a SQL backend or something, so you might sound even more talented. :)
I'm guessing that you had the term LAMP (Linux, Apache, MySQL, and PHP) in mind? To my knowledge there is no such abbreviation for HTML, CSS, and JavaScript. The easiest way to say it is to just say it.
Versus "Front end" – I think that term implies that you built something that customers used. "Web application" is nonspecific about who the users are, so it would apply to customer-facing applications as well as internal-use applications. The word "application" implies that it's not just a tool; there are users who are not the programmers. "Front end" is probably more impressive because a customer-facing application has to be nicer than an internal one.
If you are not using it in a browser, or it's not actually on the web, maybe just your intranet or an internally distributed application bundle, it's still an application developed with web technologies.