A blockchain protocol is a fascinating concept. Let’s use a relatable example. If you are reading this article I will assume that you have a smartphone. Within your smartphone you use apps like Lyft, game(s), Instagram, PayPal, so on and so forth. If you use an iPhone, iOS is the operating system. If you are using an Android, Google is the operating system.
The above apps you are using have been built to the standards of the relevant operating system that your phone supports. i.e. The Lyft app that runs on iOS, is built somewhat differently than the app that is built on Google. In the blockchain world, there are protocols that can have apps built on top of them. The operating system comparison is the best analogy I can draw. By no means am I saying they are similar in virtue, technology or in how they are built.
Blockchains can have a wider purpose than just transacting crypto: they can function as a protocol on which applications can be built. These applications are called DApps (Decentralized Application), pronounced D-App or Dapp. Examples of such protocols are Ethereum, Neo, Cardano and others. Each of these protocols also have a cryptoasset tied to them, just like Bitcoin (technology) and bitcoin (cryptoasset).