Parameters are extremely helpful in making server routes dynamic and able to respond to different inputs. Route parameters will match anything in their specific part of the path, so a route matching /monsters/:name would match all the following request paths:

/monsters/hydra
/monsters/jörmungandr
/monsters/manticore
/monsters/123

In order for a request to match a route path, it must match the entire path, as shown in the diagram to the right. The request arrives for /expressions/1. It first tries to match the /expressions route, but because it has additional path segments after /expressions, it does not match this route and moves on to the next. It matches /expressions/:id because :id will match any value at that level of the path segment. The route matches, so the Express server calls the callback function, which in turn handles the request and sends a response.