Welcome to today's Express.js lesson about Route and Query Parameters. Both play pivotal roles in handling HTTP requests in web applications. Imagine sending a letter; the street address (Route Parameter) is essential, while "Attn: Tim" (Query Parameter) is optional. Now, let's dive into these exciting terms.

In web requests, route parameters come directly in the URL, serving as "placeholders" for actual values — they guide the requests, much like a GPS guiding a vehicle. On the flip side, query parameters send extra, optional information. They come after a ? in a key=value format.

In the above URL, 123 and photos denote route parameters, while year=2021 implies a query parameter.

In Express.js, we create Route Parameters in the path of the route using a colon :. Use req.params to fetch them in the route handler function: