How do we best communicate the meaning of fathom as a protocol?

Question

What does it mean to create a protocol that others can build structures on top of? Are there any analogies that are helpful? And if protocol is a layer, what layers are above and below?

Motivation/Context:
This is a pretty heavy concept. What does it mean to create a protocol? How does building a protocol differ from building an app that runs on that protocol? What can we do to help readers understand this?

Links

Text:

"Fathom is a cryptoeconomic protocol for creating globally recognized credentials. It is implemented in a collection of solidity smart-contracts, and deployed to Ethereum."

"Fathom aims to enable a new open learning ecosystem. On top of it you can create new structures for learning, things like schools, tutoring systems, or peer-to-peer learning networks."

Suggestions

In order to not interrupt the flow of this passage, there ought to be a link to another resource. Or perhaps a brief explainer box with a link to additional resources.

Edited by Michiya