Paid Listing
A listing on a SERP that is achieved through outbidding competitors (as in PPC). The term is sometimes also used to refer to keyword-targeted advertisements, where the advertiser pays the search engine a fixed amount to have its ad shown on the SERP for a specific keyword.

Page Rank
A proprietary numerical score that is assigned by Google to every web page in their index. PR for each page is calculated by Google using a special mathematical algorithm, based on the number and quality (as determined by Google) of the inbound links to the page.

Paid Inclusion - Some directories will only consider placing your URL into their database if you pay them a fee.

Yahoo charges a $299 per year evaluation fee for commercial sites. Note that this fee doesn't guarantee that your URL will be accepted and placed in the Yahoo database, but rather that Yahoo will consider your site for inclusion in a timely manner. If your site is rejected, you're just out your $299. But you do have an opportunity to appeal the decision.

Penalty
A punishment levied against a web page by a search engine as a result of using an SEO tactic that it doesn't approve of. Tactics that most often result in penalties include using hidden text, sneaky redirects, and linking to a bad neighborhood.

Pop-up / Popup / Pop Up
A new browser window (usually containing an advertisement) automatically opened when the users performs a specified action - like opening a page, clicking a link, closing a page etc.

Portal
A web site that functions as a kind of starting page or entry point to the web. Portals typically have a wide variety of features such as search, free web-based e-mail, news etc. Well-known examples include Excite and Yahoo.

PPC
This is a traffic generating method where a search engine or directory places your link in their searchable database and charges you a fee every time your URL comes up in a search and it gets clicked on. The amount of the fee that you pay is usually determined by bidding on keywords or keyphrases.

The two largest PPC search engines are Overture and Google AdWords. There are also numerous smaller PPC engines on the net, some very good a delivering affordable targeted traffic, others not.

PR0 / PR zero
PageRank zero. A penalty (rumored to be) imposed by Google on sites caught spamdexing. It's worth noting that Google denies having such a penalty.

Promotion
In the context of search engines it refers to submitting of the site information with the intent of getting the search engine to list the site.