To access the Equivalent Domains tab, launch your Account Settings and click the third tab over from the left:
At times, you might find adding a domain equivalency to be helpful, such as when a site’s login box is in an IFRAME on another domain. If you access multiple websites of a single provider, adding these sites as equivalent domains allows you to use just one username and password set.
You can delete an equivalent domain at any time by clicking ‘Delete’ next to the entry.
The equivalent domains shown in the above image are those stored by default by LastPass.