What is a Segment
A segment is a section of your contacts based on rules.
For example you can use a segment to pull out all contacts from your list who have a .co.uk email address, or who have a birthday in a specific month, or who have never opened one of your emails.
You can segment contacts based on their data (Email address, custom fields) or their activity (Campaigns opened, links clicked, etc).
Segmenting contacts is useful for things like sending campaigns. For example you could send a campaign only to people who have a birthday in July, who have not opened an email, who have purchased something, the list goes on.
And you can add multiple rules to a segment. So you could say I want only contacts with a hotmail address who have purchased a product, who's eye colour is blue, and who are born in July.
It's a very powerful tool, and it's often quite complicated to put segments together.
Fortunately the Segment Tool has been designed to make life very easy when putting segments together