A segment is a subset of Analytics data. For example, of your whole set of users, one segment might be users from a specific country or city. Another segment might be users who purchase a special line of products or who visit a particular part of your website.
Another term that relates to this is Sections. Sections let you separate and divide those subsets of data so you can examine and respond to the element trends in your business.
For example, if you find that users from a particular geographic area are no great buying a line of products in the same volume as they usually have, you can see whether a competing business is giving the same types of goods at cheaper prices. If that set out to be the case, you could return by giving a loyalty discount to these users that underprice from your competitor’s prices. You can also use the segments as the basis for the public. For example, you might build a segment of users who visit your menswear pages and then target just those users (audience) with a remarketing drive that is centered on the new items that you are continuing to those pages.