The Blogroll
A blogroll is a list of other blogs that the writers of a given blog read on a regular basis. Usually this is listed in a sidebar or seperate page of the a blog.
In the earlier days of blogging, this was more emphasis placed on this. It was also common for bloggers to trade links in their blogrolls in an effort to increase cross polination and search engine rankings. With the proliferation of blogging as a mainstream media form, the blogroll is something that has faded into the visual language of blogging. Some bloggers point out that it's not a major source of traffic.
It is fairly common for blogrolls these days to be largely ignored by readers. However, it remains a notable convention that is part of blogging culture. Blogroll links will be seen mostly by technorati and google blog search which will increase a technorati ranking.
Blogrolls are often syndicated using OMPL, allowing a publisher to export their subscriptions from a news reader to blogging software. Here is an example of exporting and importing the OPML using Net News Wire? and Wordpress:
Violating the Ethos
Link trading as it used to exist is now the pre-eminent domain of spambots and splogs. This is not a world any blog wants to be associated with. It is considered improper to do a tit-for-tat trade of links, simply for the sake of links. This is not what readers expect and it violates the trust and authenticity that a blog implies. In fact, searching google for "Link trading" turns of many for-pay services, a good indication that link trading is not on the up and up.
Requesting a link point-blank without any relevant content to back it up is not the proper way to get a link.
See also: Link Trading - Any Real Value?