If you are adding a Shared List to a Segment, you are forced to decide: Make a Local Copy or Add Shared List? 

First, let's back up. As a refresher:

• A Shared List is a static list of contacts that you can add to multiple segments. You can find out more about Shared Lists in this Oracle document.
• A Segment is a dynamic group of contacts that you use to send a Campaign. You can add contacts by uploading to a Segment, using filter criteria, or adding a Shared List to the Segment. Find more about Segments in this Oracle document. 
• To send a Campaign, you must have a Segment. You cannot send to a Shared List.
• A Shared List can be put into a Segment, but you cannot put a Segment into a Shared List (unless you export and reimport contacts).

To add a Shared List to a Segment, create a new Segment (under Audience > Segments), save your file in your folder, and click the plus sign:

Once you have navigated to and selected your Shared List, you Eloqua will ask you if you would like to add the list as a copy (Make a Local Copy) or a connected list (Add Shared List). Here are the differences:

• If you Make a Local Copy, you are creating a carbon copy of the Shared List, at exactly that time and pasting that copy (all of the contacts in your Shared List) into your segment. Any changes made to your Shared List after this copy is made will not be reflected in your Segment. It's a snapshot in time of your Shared List. Additionally, any changes you make to this copy of your Shared List will not affect the original Shared List.
• If you select Add Shared List, you are creating an ongoing connection between the Shared List and this Segment. This means that any changes you make to your Shared List will be reflected in this Segment and vice versa. So, if you decide to add or delete a contact to your Shared List, it will update in your Segment, too. Additionally, if you remove a contact from this step of your Segment, it will also be removed from your Shared List.