Good job, Jessica!
Most social networks are walled gardens, only allowing registered users to interact or even see the content. ActivityPub provides a standard way for both clients (mobile and desktop apps, etc.) to speak to servers and different servers of any kind of social network to speak to each other. This will allow users a greater freedom as they won't be locked in to any paticular service, just because it's where their friends are. Mastodon, a microblogging social network with over a million registered users, has already implemented it!
She also thanked her fellow editors who have put a lot of endeavor for writing the spec: "It's taken many years of work by myself, Chris Webber and many people in the Social Working group. I'm thankful to all of those who helped bring this forward. I hope this standard will help shape social applications allowing them to be more open."