Clipboard is essentially OneClip, a Microsoft Garage app that oddly disappeared a few months into its development. Clipboard is being built directly into the OS with the Fall Creators Update, and when hooked up to a Microsoft Account it will allow you to share content copied on one machine with your other Windows 10 devices, as well as iOS and Android.
Clipboard is a fast and easy way to copy and paste just about anything between connected devices, whether you're on a Windows PC or your favorite mobile phone. Just hit copy on what you want to grab; your photo, map link, paragraph, even an animated gif; and it is ready to paste into whatever you want.
Windows Insiders will be able to test out Clipboard during the next few weeks, with the feature expected to ship officially in this fall alongside the appropriately named Fall Creators Update. This is a feature many Insiders have been asking for ever since OneClip was unveiled, and now it's being built directly into Windows 10.