Sample Package.xml:

<?xml version="1.0" encoding="UTF-8"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
    <types>
        <members>Listing__c</members>
        <name>CustomTab</name>
    </types>
<version>65.0</version>
</Package> 

Here, Listing__c is the Custom Object API Name.

CustomTab is also used for fetching Web Tab and Visualforce Tab.