If you have ever felt out of your depth in a discussion about email marketing, rest assured you are not alone.
The top twenty common email marketing terms and definitions below will help you expand your email marketing vocabulary and make you look and feel like an expert.

Above-the-fold — The part of a web page that is visible without scrolling. It is generally more desirable placement on a Website because of its visibility.

CPM (or "Cost per thousand") — In e-mail marketing, CPM commonly refers to the cost per 1000 names on a given rental list. For example, a rental list priced at $250 CPM would mean that the list owner charges $.25 per e-mail address.

CTR (or "Click-through rate") — The percentage (the number of unique clicks divided by the number that were opened) of recipients that click on a given URL in your e-mail.

Conversion rate — The number or percentage of recipients who respond to your call-to-action in a given e-mail marketing campaign or promotion. This is the measure of your e-mail campaign's success. You may measure conversion in sales, phone calls, appointments etc.

E-mail blocking — E-mail blocking typically refers to blocking by ISPs. E-mails that are blocked are not processed through the ISP and are essentially prevented from reaching their addressed destination. ISPs actively block email coming from suspected spammers.

Email newsletter ads or sponsorships — Buying ad space in an email newsletter or sponsoring a specific article or series of articles. Advertisers pay to have their ad (text, HTML or both depending on the publication) inserted into the body of the email.

Email newsletter ads and sponsorships allow advertisers to reach a targeted audience driving traffic to a website, store or office, signups to a newsletter or sales of a product or service.

Hard bounce/Soft bounce — A hard bounce is the failed delivery of an e-mail due to a permanent reason like a non-existent address. A soft bounce is the failed delivery of an e-mail due to a temporary issue, like a full mailbox or an unavailable server.

House list (or "Retention list") — A permission-based list that you built yourself. Use it to market, cross sell and up-sell, and to establish a relationship with customers over time.

Your house list is one of your most valuable assets because it is 7 times less expensive to market to an existing customer than it is to acquire a new one. Use every opportunity to add to it and use it.

HTML e-mail — An e-mail that is formatted using Hypertext Markup Language instead of plain text. HTML makes it possible to include unique fonts, graphics and background colors.

HTML makes an e-mail more interesting and when used properly can generate higher response rates than plain text.

Open rate — The percentage of e-mails opened in any given e-mail marketing campaign, or the percentage opened of the total number of e-mails sent.

Opt-in (or "Subscribe") — To opt-in or subscribe to an e-mail list is to choose to receive e-mail communications by supplying your e-mail address to a particular company, website or individual thereby giving them permission to e-mail you. The subscriber can often indicate areas of personal interest (e.g. mountain biking) and/or indicate what types of e-mails she wishes to receive from the sender (e.g. newsletters).

Opt-out (or "Unsubscribe") — To opt-out or unsubscribe from an e-mail list is to choose not to receive communications from the sender by requesting the removal of your e-mail address from their list.

Permission-based e-mail — E-mail sent to recipients who have opted-in or subscribed to receive e-mail communications from a particular company, website or individual.

Permission is an absolute prerequisite for legitimate and profitable e-mail marketing.

Privacy policy — A clear description of a website or company's policy on the use of information collected from and about website visitors and what they do, and do not do, with the data.

Your privacy policy builds trust especially among those who opt-in to receive e-mail from you or those who register on your site. If subscribers, prospects and customers know their information is safe with you, they will likely share more information with you making your relationship that much more valuable.

Rental list (or "Acquisition list") — A list of prospects or a targeted group of recipients who have opt-in to receive information about certain subjects. Using permission-based rental lists, marketers can send e-mail messages to audiences targeted by interest category, profession, demographic information and more. Renting a list usually costs between $.10 and $.40 per name.

Be sure your rental list is a certified permission-based, opt-in list. Permission-based lists are rented, not sold. Don't be fooled by a list offer that sounds too good to be true. Save the $19.95 and buy yourself a George Foreman grill instead. Unlike the cheap list, the grill is worth the money.

Signature file (or "Sig file" for short) — A tagline or short block of text at the end of an e-mail message that identifies the sender and provides additional information such as company name and contact information.

Your signature file is a marketing opportunity. Use it to convey a benefit and include a call-to-action with a link.

Spam or UCE (Unsolicited Commercial E-mail) — E-mail sent to someone who has not opt-in or given permission to the sender.

Do you get spam? (a rhetorical question, to be sure) Find out how the sender obtained your e-mail address.

Targeting — Selecting a target audience or group of individuals likely to be interested in a certain product or service.

Targeting is very important for an e-mail marketer because targeted and relevant e-mail campaigns, yield a higher response and result in fewer unsubscribes.

URL (or "Universal Resource Locator") — A website, page or any other document address or location on the Internet. URLs indicate the location of every file on every computer accessible through the Internet.

Viral Marketing — A type of marketing that is carried out voluntarily by a company's customers. It is often referred to as word-of-mouth advertising. Email has made this type of marketing very prevalent. Tools such as "send this page, article or website to a friend" encourage people to refer or recommend your company product, service or a specific offer to others.