Many web sites, in particular ones that serve content from a content management system or database, deliver their content as HTML with an underlying computer generated structure that is then visually formatted and styled using Cascading Style Sheets (CSS) and JavaScript.

Additionally, when the website uses a web form to query and return results, the web address is read by the web server or application server, the address is then parsed for parameters, and the parameters are passed to the database behind the website which control the results returned.

There are techniques that utilize these facts to extract large amounts of data from the backend database behind a website through a series of crafted web page requests.

Collectively these techniques are called Web Scraping.

Two of the key techniques of web scraping are URL Hacking and HTML parsing.