The title is different from the name of the app.
the name normally use a reverse domain name and looks something like com.google.something.appname. This is the unique identifier of the apps
EDIT: Just for curiosity, the facebook app name is com.facebook.katana.
EDIT2: To sum up: the package name is what identifies the apps, not the title, so you can have multiple apps with the name facebook, but only one with com.facebook.katana, so you can have two apps named facebook in your mobile. But if you upload an app with the name facebook to google play, will be blocked because it is well-known app from a company, and could be a scam. It won´t apply however to common names like "weather".
If your app displays the brand, icon, or title from another app in order to get users to download your app, you are leading users to believe that your app is developed by the same entity as the other app and offers similar content or experience. This is an impersonation of the other app and developer, and it is a violation of Google Play’s policies. If you publish apps that violate impersonation policies, your apps can be suspended and your developer account terminated.
Finally, if you want to change the packet name of your app, you can do it in adroid studio as posted here