A deployed application component is a runnable component that is deployed to a compute resource (e.g. AWS EC2 server).
In the context of Chef Habitat, this would be equivalent to a Chef Habitat package that's deployed and running as a service under the Chef Habitat Supervisor.
Each time an application component is deployed to a compute resource, it will count towards the number of total application components that can be deployed under your usage tier.
For instance, if you have a database application component that you wish to deploy onto three compute resources to create a database cluster, each deployed database application component will count towards your total of allowed deployed application components under your usage tier.