According to Wikipedia, it's a special usage of email allowing distribution of information to many people. It's a list of email addresses that your business might use to notify people of your sales and events. Many people use them to sell their products and services.
An email list can be a simple computer file that contains a list of email addresses. This list can be copied into the "To:" box of an outgoing email. This enables you to send a single email to many people at one time. This method is only recommended if you have a small number of addresses in your list. If you have less than 100 addresses this method can work. A better method is to use an email marketing service. Some of the common ones include Aweber, Constant Contact, and Mail Chimp. There are many others. See below for a list of some popular ones.
Email marketing is a marketing method using an email system to market products and services to an email list.
The first challenge with email marketing is building the list. You need email addresses in your list. The more the better.
The most common way to get email addresses added to an email list is to include an email signup form on a website. All of the email services provide the capability to create your own forms with instructions for putting them on a website. The forms can also be hosted at the email service company. In that case you would simply need a clickable link on your website that brings a visitor to the form.
You can also ask your customers for their email addresses and enter them into your email system yourself. Include a spot for customers to enter their email addresses on various forms that you have in your place of business.
When a person signs up to be on your list they will normally get an email in response. That email welcomes them to the list and often asks them to click a link to confirm that they requested to be on the list. This process is called double opt in. Many people highly recommend using double opt in but there are some very successful email marketers who disagree saying that you should only require the signup and not the secondary opt in.
Usually there will be several follow up email messages, previously set up, to be sent out over a period of weeks to months after a person signs up.
Email marketing services also provide the ability to send what they call broadcast messages. These are emails that can be created and sent to the email list just as follow up messages are. the difference is that follow up messages are set up ahead of time. Broadcast messages are set up shortly before they are sent. Broadcast messages are sent to everyone on the list. Follow up messages are sent individually to a single email address at specified times after sign up.