If you're developing a Facebook app - either a game or simply an app to allow users to log in with their Facebook accounts on your website or mobile app, you're asked to have a Terms of Service agreement for the "Terms of Service URL" field.
This requirement from Facebook is optional when you want to make your app live, i.e. no longer in development mode.
Facebook is asking all apps to have a Terms of Service agreement before the app is public to users.
Depending on your app, your app may not be approved to go live if you don't have the "Terms of Service URL set" field with an URL to your agreement.
Here's how to the "Terms of Service URL" field looks. This is where you need to add the URL:
Here's how to find the "Terms of Service URL" field:
You need to host the Terms of Service agreement on your own website. Facebook will not provide hosting.
If you only developed a Facebook app to be used as a social login for your users, i.e. Sign-in with Facebook functionality, link the Terms of Service from your website to the Facebook app in the "Terms of Service URL" field.
This is exactly what Buffer did.
The same link from the "Login Dialog" is present on Buffer's website footer:
Deer Hunter, a Facebook game from Glu, links their Terms of Service for the game with their Terms of Service agreement found on their website. This is how the link appears in Facebook App Store:
The same link to their Terms of Service is available on their website at the footer section:
Please note that a "Terms of Service" is the same as a "Terms and Conditions". The names for this kind of agreement can be any of the following: