The act of forming a personal connection with someone/something (object) unidirectionally/asymmetrically to get updates pushed to.
Related actions:
- [FollowAction](http://schema.org/FollowAction): Unlike FollowAction, SubscribeAction implies that the subscriber acts as a passive agent being constantly/actively pushed for updates.
- [RegisterAction](http://schema.org/RegisterAction): Unlike RegisterAction, SubscribeAction implies that the agent is interested in continuing receiving updates from the object.
- [JoinAction](http://schema.org/JoinAction): Unlike JoinAction, SubscribeAction implies that the agent is interested in continuing receiving updates from the object.