The Application Repository is a central location for storing, managing, and distributing custom applications developed on the Now Platform.

From Developer Site > App Repo :

“The ServiceNow Application Repository stores custom applications and enables developers to distribute applications across multiple instances in their organization.”

A workflow is a tool that allows you to automate processes on the ServiceNow platform. A workflow consists of activities and transitions that define the logic and flow of the process. A workflow context is an instance of a workflow that is generated from a workflow version, executes activities, and follows transitions. A workflow context is associated with a specific record on a table and tracks the state and progress of the workflow. You can view and manage the workflow contexts from the Workflow Contexts module or the Workflow Contexts related list on a record.

The other options are not valid definitions of a workflow context. A checked out workflow is a workflow that is being edited by a user and has not been published yet. The table and conditions for a workflow are the criteria that determine when a workflow should run on a record. The business reason or process for a workflow is the purpose and function of the workflow.