If you want to email a group of people without having to type in their email addresses every time, several group email options are available.
A Google Group has an email address (e.g. firstname.lastname@example.org). Emails sent to the list are delivered to each recipient's inbox. Along with their use for email, groups are also an easy way to assign permissions within Google to a group of people, such as the ability to view a Google Calendar or Document. There is no inbox for a Google Group, but Groups can be set up to archive messages, which can be read on the webpage dedicated to the Group.
A Listserv has an email address ending in listserv.brown.edu (for example, email@example.com). Emails sent to the list are delivered to each recipient's inbox. These lists are configurable by the list owners and are used to distribute mail among subscribers. A benefit of Listservs is that a lot of people are familiar with subscribing and unsubscribing to them, so they are appropriate to use when you want people to easily join and leave the list.
A shared mailbox has an email address (e.g. firstname.lastname@example.org). Emails sent to the address will be delivered to the shared mailbox (not to individual recipients). People who have been given access to the shared mailbox will have to remember to check the mailbox for new mail.
A contact group is created within your contacts and only visible by you (or if it's in a shared mailbox, whoever has access to the mailbox). A contact group does NOT have a unique email address that cannot be emailed by others. It's a very lightweight, quick solution but has limitations.
Class Discussion List
A Class Discussion List provides instructors with an email address that sends mail to their class roster. The Class Discussion List may be used for two-way email discussion between instructors and students in a course.
Class Announcement List
A Class Announcement List enables instructors to send one way (no-reply) email messages to their students.
This service is used by high level University offices to send official email communications to large, specified segments of the University population.