Broadly defined, parking (also called domain parking) is the registration of a domain name without using it to house a website, or for services like email, and without otherwise placing any content on the domain. Domain parking uses range from simply reserving a domain for future development to questionable practices like cybersquatting.
Parking is generally divided into two major categories, monetized and non-monetized parking. In non-monetized parking, domain registrars may or may not display a message indicating that the website is soon to launch or currently being built; such a message might also be displayed by the ultimate registrant, as well. In monetized parking, an advertising technique used primarily by domain registrars, domain speculators and Internet advertising publishers, the domain name will display a series of advertisements and links, with the domain holder being paid on any variety of criteria, like the number of clicks, exposures or searches generated by their parked pages.
Once-active domains that formerly housed websites are often prized for the purposes of parked domain monetization, as many expired domains will still have maintain many of the inbound links that existed during the life span of the website previously housed on the domain.