Crashplan Central is the feature that allows you to use their servers as a backup destination:
CrashPlan Central is the cloud backup destination for CrashPlan+, providing online storage for your personal files in our secure data centers located around the world.
It costs money (as part of Crashplan+ or up). Crashplan itself is free for backups to other systems on your local network (or your own servers somewhere).
It's a significantly distinct subset of the program's functionality and the tag is useful if you're specifically asking about the central online storage. Something comparable would probably be outlook-web-access.