Dynamic: These are what the previous explanation of “messy URLs” really come from. Dynamic URLs are the end result of database queries that provide content output based on the result of that query. The URL ends up looking quite garbled, aka “messy”, and often includes the following characters: ?, &, %, +, =, $. Dynamic URLs are often found as part of consumer-driven websites: shopping, travel, or anything that requires changing answers for many different user queries.

via What Is a URL? – Definition of Uniform Resource Locators