What does it mean when a site asks to "Manage your contacts" when signing in with Google account?

[TroyOi]

These days, many third-party sites allow you to sign in via one's Google (or Facebook, or Twitter, etc.) account. In the past, I have not been in the habit of looking closely at the permissions that they ask you to grant before signing in. But I just noticed one site asking for permission to "manage" my Google contacts. What does that mean?? Will they actually be able to edit my contacts? (If they just want to see my contacts, why the word "manage".)

BTW, what also amazes me is the apparent dearth of information on this subject. With all the concern about privacy these days, you would think that Google would have an easily accessible page that explains precisely what permissions third party sites might request, and what those permissions might mean. But after searching, I can find precious little on the subject.