Conceptually and in simple terms, what is a "deployment"? Is it a place where the code runs? Is it a snapshot of the code, or some bundling of the flow with configuration? How does the concept of a "deployment" click with the general idea of workers and work queues?

Good question.

Deployments are server-side representations of flows. They store the crucial metadata needed for remote orchestration including when, where, and how a workflow should run. Deployments elevate workflows from functions that you must call manually to API-managed entities that can be triggered remotely

from: https://docs.prefect.io/latest/concepts/deployments/ With

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, you can create a deployment that doesn’t use a worker. We’ll be exploring deployments in depth tomorrow.