This name is an acronym for Uniform Resource Locator. It is a unique address, of which there can be only one across the whole internet. Something like human DNA on the internet.
URL is sometimes confused with URI. They are practically the same thing, except that in URI the I at the end stands for Identifier, and it includes URL.
A URL has several parts. It is the protocol (http), the domain (seznam) and the top-level domain (.cz). A URL is thus a human-readable address of a web page or file.
The address bar always shows the current address of the page you are on. Because the address is unique, you can enter it in any browser and always get the same page. Since addresses do not change, you can save a link to a web page and view it again later.
Well-formed URLs pointing to other pages are important for search engines, which can use them to derive relationships and connections between web pages.